U.S. patent application number 14/401394 was filed with the patent office on 2015-05-07 for optoelectronic device comprising porous scaffold material and perovskites.
The applicant listed for this patent is ISIS INNOVATION LIMITED. Invention is credited to Michael Lee, Henry Snaith.
Application Number | 20150122314 14/401394 |
Document ID | / |
Family ID | 48468670 |
Filed Date | 2015-05-07 |
United States Patent
Application |
20150122314 |
Kind Code |
A1 |
Snaith; Henry ; et
al. |
May 7, 2015 |
OPTOELECTRONIC DEVICE COMPRISING POROUS SCAFFOLD MATERIAL AND
PEROVSKITES
Abstract
The invention provides an optoelectronic device comprising: (i)
a porous dielectric scaffold material; and (ii) a semiconductor
having a band gap of less than or equal to 3.0 eV, in contact with
the scaffold material. Typically the semiconductor, which may be a
perovskite, is disposed on the surface of the porous dielectric
scaffold material, so that it is supported on the surfaces of pores
within the scaffold. In one embodiment, the optoelectronic device
is an optoelectronic device which comprises a photoactive layer,
wherein the photoactive layer comprises: (a) said porous dielectric
scaffold material; (b) said semiconductor; and (c) a charge
transporting material. The invention further provides the use, as a
photoactive material in an optoelectronic device, of: (i) a porous
dielectric scaffold material; and (ii) a semiconductor having a
band gap of less than or equal to 3.0 eV, in contact with the
scaffold material. Further provided is the use of a layer
comprising: (i) a porous dielectric scaffold material; and (ii) a
semiconductor having a band gap of less than or equal to 3.0 eV, in
contact with the scaffold material; as a photoactive layer in an
optoelectronic device. In another aspect, the invention provides a
photoactive layer for an optoelectronic device comprising (a) a
porous dielectric scaffold material; (b) a semiconductor having a
band gap of less than or equal to 3.0 eV, in contact with the
scaffold material; and (c) a charge transporting material.
Inventors: |
Snaith; Henry; (Oxfordshire,
GB) ; Lee; Michael; (Oxfordshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ISIS INNOVATION LIMITED |
Oxford |
|
GB |
|
|
Family ID: |
48468670 |
Appl. No.: |
14/401394 |
Filed: |
May 20, 2013 |
PCT Filed: |
May 20, 2013 |
PCT NO: |
PCT/GB2013/051307 |
371 Date: |
November 14, 2014 |
Current U.S.
Class: |
136/255 |
Current CPC
Class: |
H01L 51/4213 20130101;
H01L 31/0324 20130101; H01L 51/0032 20130101; Y02E 10/549 20130101;
H01L 51/422 20130101; H01L 51/4226 20130101; H01L 2031/0344
20130101 |
Class at
Publication: |
136/255 |
International
Class: |
H01L 51/42 20060101
H01L051/42; H01L 31/032 20060101 H01L031/032 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2012 |
GB |
1208794.6 |
Jun 13, 2012 |
GB |
1210489.9 |
Claims
1. A photovoltaic device comprising: (i) a porous dielectric
scaffold material having a band gap of equal to or greater than 4.0
eV; and (ii) a perovskite semiconductor having a band gap of less
than or equal to 3.0 eV, in contact with the scaffold material.
2. A photovoltaic device according to claim 1 wherein said
perovskite semiconductor comprises at least one halide anion.
3. A photovoltaic device according to claim 1 wherein the
perovskite semiconductor has a band gap of less than or equal to
2.8 eV, preferably less than or equal to 2.5 eV, and optionally
less than or equal to 2.0 eV.
4. A photovoltaic device according to claim 1 wherein the
perovskite semiconductor is disposed on the surface of said porous
dielectric scaffold material, and preferably the perovskite
semiconductor is disposed on the surfaces of pores within said
dielectric scaffold material.
5. (canceled)
6. A photovoltaic device according to claim 1 wherein the
dielectric scaffold material comprises an oxide of aluminium,
germanium, zirconium, silicon, yttrium or ytterbium; or alumina
silicate.
7. A photovoltaic device according to claim 1 wherein the
dielectric scaffold material comprises porous alumina, and
preferably mesoporous alumina.
8. (canceled)
9. A photovoltaic device according to claim 1, wherein the porosity
of said dielectric scaffold material is equal to or greater than
50%.
10. A photovoltaic device according to claim 1 wherein the porous
dielectric scaffold material is mesoporous
11. A photovoltaic device according to claim 1 wherein the
perovskite semiconductor is also a photosensitizing material
12. A photovoltaic device according to claim 1 wherein the
perovskite semiconductor is any one of an n-type semiconductor, a
p-type semiconductor, and an intrinsic semiconductor.
13-16. (canceled)
17. A photovoltaic device according to claim 2 wherein the
perovskite comprises a first cation, a second cation, and said at
least one halide anion.
18. A photovoltaic device according to claim 17 wherein the second
cation is a metal cation, and preferably the metal cation is
selected from Sn.sup.2+ and Pb.sup.2+.
19. (canceled)
20. A photovoltaic device according to claim 17 wherein the first
cation is an organic cation, and preferably the organic cation has
the formula (R.sub.5NH.sub.3)+, wherein R.sub.5 is hydrogen, or
unsubstituted or substituted C.sub.1-C.sub.20 alkyl.
21. (canceled)
22. A photovoltaic device according to claim 1 wherein the
perovskite is a mixed-anion perovskite comprising a first cation, a
second cation, and two or more different anions selected from
halide anions and chalcogenide anions.
23. A photovoltaic device according to claim 22 wherein the
perovskite is a mixed-halide perovskite, wherein said two or more
different anions are two or more different halide anions.
24. A photovoltaic device according to claim 1 wherein the
perovskite is a perovskite compound of formula (I): [A][B][X].sub.3
(I) wherein: [A] is at least one organic cation; [B] is at least
one metal cation; and [X] is said at least one anion.
25. A photovoltaic device according to claim 24 wherein [X] is two
or more different anions selected from halide anions and
chalcogenide anions, and preferably [X] is two or more different
halide anions.
26. (canceled)
27. A photovoltaic device according to claim 1 wherein the
perovskite is a perovskite compound of the formula (IA):
AB[X].sub.3 (IA) wherein: A is an organic cation; B is a metal
cation; and [X] is two or more different halide anions
28. A photovoltaic device according to claim 1 wherein the
perovskite is a perovskite compound of formula (II):
ABX.sub.3-yX'.sub.y (II) wherein: A is an organic cation; B is an
metal cation; X is a first halide anion; X' is a second halide
anion which is different from the first halide anion; and y is from
0.05 to 2.95.
29. A photovoltaic device according to claim 11, wherein the
perovskite is selected from CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3SnBrI.sub.2,
CH.sub.3NH.sub.3SnBrCl.sub.2, CH.sub.3NH.sub.3SnF.sub.2Br,
CH.sub.3NH.sub.3SnIBr.sub.2, CH.sub.3NH.sub.3SnICl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2I, CH.sub.3NH.sub.3SnClBr.sub.2,
CH.sub.3NH.sub.3SnI.sub.2Cl and CH.sub.3NH.sub.3SnF.sub.2Cl.
30. (canceled)
31. A photovoltaic device according to claim 1 which comprises a
photoactive layer, which photoactive layer comprises: said porous
dielectric scaffold material; and said perovskite
semiconductor.
32. A photovoltaic device according to claim 1 which further
comprises a charge transporting material
33. (canceled)
34. A photovoltaic device according to claim 32 wherein the charge
transporting material is a hole transporting material.
35. A photovoltaic device according to claim 34 wherein the hole
transporting material is a polymeric or molecular hole
transporter.
36. A photovoltaic device according to claim 34 wherein the hole
transporting material is selected from spiro-OMeTAD, P3HT, PCPDTBT
and PVK.
37. A photovoltaic device according to claim 34 wherein the hole
transporting material is an inorganic hole transporter, and
preferably the inorganic hole transporter is CuI, CuBr, CuSCN,
Cu.sub.2O, CuO or CIS.
38. (canceled)
39. A photovoltaic device according to claim 32 wherein the charge
transporting material is an electron transporting material, and
preferably the electron transporting material comprises a fullerene
or perylene, or derivatives thereof, or P(NDI2OD-T2).
40. (canceled)
41. A photovoltaic device according to claim 32 wherein the charge
transporting material comprises a perovskite.
42-43. (canceled)
44. A photovoltaic device according to claim 41 in which said
semiconductor comprises a first perovskite, wherein the first
perovskite is as defined in claim 1, and said charge transporting
material comprises a second perovskite, wherein the first and
second perovskites are the same or different.
45. (canceled)
46. A photovoltaic device according to claim 41 wherein the
perovskite of the charge transporting material is a perovskite
comprising a first cation, a second cation, and at least one
anion.
47. A photovoltaic device according to claim 41 wherein the
perovskite of the charge transporting material is a perovskite
compound of formula (IB): [A][B][X].sub.3 (IB) wherein: [A] is at
least one organic cation or at least one group 1 metal cation; [B]
is at least one metal cation; and [X] is said at least one
anion.
48. A photovoltaic device according to claim 47 wherein [A]
comprises Cs+.
49. A photovoltaic device according to claim 47 wherein [B]
comprises Pb.sup.2+ or Sn.sup.2+.
50. (canceled)
51. A photovoltaic device according to claim 47 wherein [X]
comprises a halide anion or a plurality of different halide
anions.
52. (canceled)
53. A photovoltaic device according to claim 47 wherein the
perovskite compound of formula (IB) is CsPbI.sub.3 or
CsSnI.sub.3.
54. (canceled)
55. A photovoltaic device according to claim 47 wherein the
perovskite compound of formula (IB) is CsPbI.sub.2Cl,
CsPbICl.sub.2, CsPbI.sub.2F, CsPbIF.sub.2, CsPbI.sub.2Br,
CsPbIBr.sub.2, CsSnI.sub.2Cl, CsSnICl.sub.2, CsSnI.sub.2F,
CsSnIF.sub.2, CsSnI.sub.2Br or CsSnIBr.sub.2.
56. (canceled)
57. A photovoltaic device according to claim 47 wherein: [X] is as
defined in claim 25; and/or [A] comprises an organic cation as
defined in claim 20; and/or [B] comprises a metal cation as defined
in claim 18.
58. A photovoltaic device according to claim 41 wherein the
perovskite of the charge transporting material is a perovskite as
defined in any one claim 17.
59. A photovoltaic device according to claim 32 wherein the charge
transporting material is disposed within pores of said porous
dielectric scaffold material.
60. A photovoltaic device according to claim 32 which comprises a
photoactive layer, wherein the photoactive layer comprises: said
porous dielectric scaffold material; said perovskite semiconductor;
and said charge transporting material.
61-64. (canceled)
65. A photovoltaic device according to claim 60 which photoactive
layer comprises a layer comprising said porous dielectric scaffold
material and said perovskite semiconductor, wherein the perovskite
semiconductor is disposed on the surface of pores within said
dielectric scaffold material, and wherein said charge transporting
material is disposed within pores of said porous dielectric
scaffold material.
66. A photovoltaic device according claim 60 which photoactive
layer comprises a layer comprising said charge transporting
material disposed on a layer comprising said porous dielectric
scaffold material and said perovskite semiconductor, wherein the
perovskite semiconductor is disposed on the surface of pores within
said dielectric scaffold material, and wherein the device further
comprises said charge transporting material disposed within pores
of said porous dielectric scaffold material.
67. A photovoltaic device according to claim 31 wherein the
thickness of the photoactive layer is from 100 nm to 3000 nm.
68. (canceled)
69. A photovoltaic device according to claim 31 which comprises: a
first electrode; a second electrode; and disposed between the first
and second electrodes: said photoactive layer; and a compact layer
comprising a metal oxide or a metal chalcogenide.
70. A photovoltaic device according to claim 69 wherein the compact
layer comprises a metal oxide or a metal sulphide, and preferably
comprises an n-type semiconductor comprising an oxide of titanium,
tin, zinc, gallium, niobium, tantalum, indium, neodymium, palladium
or cadmium, or a sulphide of zinc or cadmium.
71-74. (canceled)
75. A photovoltaic device according to claim 69 which further
comprises an additional layer, disposed between the compact layer
and the photoactive layer, which additional layer comprises a metal
oxide or a metal chalcogenide which is the same as or different
from the metal oxide or a metal chalcogenide employed in the
compact layer.
76. A photovoltaic device according to claim 75 wherein the
additional layer comprises alumina, magnesium oxide, cadmium
sulphide, silicon dioxide or yttrium oxide.
77-81. (canceled)
82. A photovoltaic device according to claim 1 wherein x is less
than or equal to 0.6 eV, and preferably less than or equal to 0.45
eV, wherein: x is equal to A-B, wherein: A is the optical band gap
of said thin-film semiconductor; and B is the open-circuit voltage
generated by the photovoltaic device under standard AM1.5G 100
mWcm.sup.-2 solar illumination.
83-91. (canceled)
92. A photoactive layer for a photovoltaic device comprising (a) a
porous dielectric scaffold material having a band gap of equal to
or greater than 4.0 eV; (b) a perovskite semiconductor having a
band gap of less than or equal to 3.0 eV, in contact with the
scaffold material; and (c) a charge transporting material.
93. A photoactive layer according to claim 92 wherein the
perovskite semiconductor is as defined in claim 2.
94. (canceled)
95. A photovoltaic device according to claim 31, wherein said
photoactive layer further comprises encapsulated metal
nanoparticles.
96. A photoactive layer according to claim 93, wherein said
photoactive layer further comprises encapsulated metal
nanoparticles.
Description
FIELD OF THE INVENTION
[0001] The invention relates to optoelectronic devices, including
photovoltaic devices such as solar cells, and light-emitting
devices.
BACKGROUND TO THE INVENTION
[0002] Over recent years, the field of optoelectronic devices has
developed rapidly, generating new and improved devices that go some
way to meeting the ever increasing global demand for low-carbon
emissions. However, this demand cannot be met with the devices
currently available. The issues with the currently-available
technology are illustrated below, using the area of photovoltaic
devices.
[0003] The leading technologies pushing to realise the ultimate
goal of low cost solar power generation are dye-sensitized and
organic photovoltaics. Dye-sensitized solar cells are composed of a
mesoporous n-type metal oxide photoanode, sensitized with organic
or metal complex dye and infiltrated with a redox active
electrolyte. [O'Regan, B. and M. Gratzel (1991). "A Low-Cost,
High-Efficiency Solar-Cell Based On Dye-Sensitized Colloidal
TiO.sub.2 Films." Nature 353(6346): 737-740.] They currently have
certified power conversion efficiencies of 11.4% [Martin A. Green
et al. Prog. Photovolt: Res. Appl. 2011; 19:565-572] and highest
reported efficiencies are 12.3% [Aswani Yella, et al. Science 334,
629 (2011)]. The current embodiment of organic solar cells, is a
nanostructured composite of a light absorbing and hole-transporting
polymer blended with a fullerene derivative acting as the n-type
semiconductor and electron acceptor [Yu, G., J. Gao, et al. (1995)
Science 270(5243): 1789-1791 and Halls, J. J. M., C. A. Walsh, et
al. (1995) Nature 376(6540): 498-500]. The most efficient organic
solar cells are now just over 10% [Green, M. A., K. Emery, et al.
(2012). "Solar cell efficiency tables (version 39)." Progress in
Photovoltaics 20(1): 12-20]. Beyond organic materials and dyes,
there has been growing activity in the development of solution
processable inorganic semiconductors for thin-film solar cells.
Specific interest has emerged in colloidal quantum dots, which now
have verified efficiencies of over 5%, [Tang, J, et al. Nature
Materials 10, 765-771 (2011)] and in cheaply processable thin film
semiconductors grown from solution such as copper zinc tin sulphide
selenide (CZTSS) which has generated a lot of excitement recently
by breaking the 10% efficiency barrier in a low cost fabrication
route. [Green, M. A., K. Emery, et al. (2012). "Solar cell
efficiency tables (version 39)." Progress in Photovoltaics 20(1):
12-20] The main issue currently with CZTSS system is that it is
processed with hydrazine, a highly explosive reducing agent [Teodor
K. Todorov et al. Adv. Matter 2010, 22, E156-E159].
[0004] For a solar cell to be efficient, the first requirement is
that it absorbs most of the sun light over the visible to near
infrared region (300 to 900 nm), and converts the light effectively
to charge. Beyond this however, the charge needs to be collected at
a high voltage in order to do useful work, and it is the generation
of a high voltage with suitable current that is the most
challenging aspect for the emerging solar technologies. A simple
measure of how effective a solar cell is at generating voltage from
the light it absorbs, is the difference energy between the optical
band gap of the absorber and the open-circuit voltage generated by
the solar cell under standard AM1.5G 100 mWcm.sup.-2 solar
illumination [H J Snaith et al. Adv. Func. Matter 2009, 19, 1-7].
For instance, for the most efficient single junction GaAs solar
cells the open circuit voltage is 1.11 V and the band gap is 1.38
eV giving a "loss-in-potential" of approximately 270 meV [Martin A.
Green et al. Prog. Photovolt: Res. Appl. 2011; 19:565-572]. For
dye-sensitized and organic solar technologies these losses are
usually on the order of 0.65 to 0.8 eV. The reason for the larger
losses in the organics is due to a number of factors. Organic
semiconductors used in photovoltaics are generally hindered by the
formation of tightly bound excitons due to their low dielectric
constants. In order to obtain effective charge separation after
photoexcitation, the semiconducting polymer is blended with an
electron accepting molecule, typically a fullerene derivative,
which enables charge separation. However, in doing so, a
significant loss in energy is required to do the work of separating
the electron and hole. [Dennler, G., M. C. Scharber, et al. (2009).
"Polymer-Fullerene Bulk-Heterojunction Solar Cells." Advanced
Materials 21(13): 1323-1338] Dye-sensitized solar cells have
losses, both due to electron transfer from the dye (the absorber)
into the TiO.sub.2 which requires a certain "driving force" and due
to dye regeneration from the electrolyte which requires an "over
potential". For dye-sensitized solar cells, moving from a
multi-electron Iodide/triiodide redox couple to one-electron
outer-sphere redox couples, such as a cobalt complexes or a
solid-state hole-conductor, improves the issue but large losses
still remain [Oregan 91, Aswani Yella, et al. Science 334, 629
(2011), and Bach 98 and Gratzel solid-state JACS]. There is an
emerging area of "extremely thin absorber" solar cells which are a
variation on the solid-state dye-sensitized solar cell.[Y. Itzhaik,
O. Niitsoo, M. Page, G. Hodes, J. Phys. Chem. C 113, 4254-4256
(2009)] An extremely thin absorber (ETA) (few nm thick) layer is
coated upon the internal surface of a mesoporous TiO.sub.2
electrode, and subsequently contacted with a solid-state
hole-conductor or electrolyte. These devices have achieved
efficiencies of up to 7% for solid-state devices employing
Sb.sub.2S.sub.3 as the absorber, [J. A. Chang et al., Nano Lett.
12, 1863-1867 (2012)] and up to 6.5% employing a lead-halide
perovskite in photoelectrochemical solar cell.[A. Kojima, K.
Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 131, 6050-6051
(2009); J-H Im, C-R Lee, J-W Lee, S-W Park, N-G Park, Nanoscale 3,
4088-4093 (2011)] However, the ETA concept still suffer from rather
low open-circuit voltages.
[0005] There is therefore a need for a new approach to developing
optoelectronic devices. New systems that combine favourable
properties such as high device efficiency and power conversion,
with device stability are required. In addition, the devices should
consist of inexpensive materials that may be easily tuned to
provide the desirable properties and should be capable of being
manufactured on a large scale.
SUMMARY OF THE INVENTION
[0006] The present inventors have provided optoelectronic devices
which exhibit many favourable properties including high device
efficiency. Record power conversion efficiencies as high as 11.5%
have been demonstrated under simulated AM1.5 full sun light.
[0007] Other characteristics that have been observed in devices
according to the invention are, for instance, surprisingly
efficient charge collection and extremely high open-circuit
voltages approaching 1.2 V. These devices show fewer fundamental
loses than comparable devices currently on the market.
[0008] These advantages have been achieved using a device which
comprises (a) a porous dielectric scaffold material and (b) a
semiconductor having a band gap of less than or equal to 3.0 eV, in
contact with the scaffold material. Typically the semiconductor is
disposed on the surface of the porous dielectric scaffold material,
so that it is supported on the surfaces of pores within the
scaffold. A charge transporting material is typically also
employed, which infiltrates into the porous structure of the
scaffold material so that it is in contact with the semiconductor
that is supported on the scaffold. The semiconductor typically acts
as a light-absorbing, photosensitising material, as well as an
charge-transporting material. When, for instance, the semiconductor
is an n-type semiconductor, the porous nanostructure of the
semiconductor/scaffold composite helps rapidly to remove the holes
from the n-type absorber, so that purely majority carriers are
present in the absorber layer. This overcomes the issue of short
diffusion lengths which would arise if the semiconductor were
employed in solid, thin-film form.
[0009] The materials used in the device of the invention are
inexpensive, abundant and readily available and the individual
components of the devices exhibit surprisingly stability. Further,
the methods of producing the device are suitable for large-scale
production.
[0010] For example, in some embodiments the inventors have taken
advantage of the properties of inorganic semiconductors by using a
layered organometal halide perovskite as the absorber, which is
composed of abundant elements. This material may be processed from
a precursor solution via spin-coating in ambient conditions. In a
solid-thin film form, it operates moderately well as a solar cell
with a maximum efficiency of 3%. However, in order to overcome the
issue of short diffusion lengths, the inventors have created the
above-mentioned nanostructured composite. In some embodiments the
scaffold is a mesoporous insulating aluminium oxide, which is
subsequently coated with the perovskite film and dried which
realises a mesoporous perovskite electrode. This may then be
infiltrated with a p-type hole-conductor which acts as to carry the
photoinduced holes out of the device. This new architecture and
material system has an optical band gap of 1.56 eV and generates up
to 1.1V open-circuit voltage under AM1.5G 100 mWcm.sup.-2 sun
light. This difference, which represents the fundamental loses in
the solar cell, is only 0.44 eV, lower than any other emerging
photovoltaic technology. The overall power conversion efficiency of
11.5% is also one of the highest reported, and represents the
starting point for this exciting technology. With mind to the very
low potential drop from band gap to open-circuit voltage, this
concept has scope to become the dominating low cost solar
technology.
[0011] Accordingly, the invention provides an optoelectronic device
comprising: (i) a porous dielectric scaffold material; and (ii) a
semiconductor having a band gap of less than or equal to 3.0 eV, in
contact with the scaffold material.
[0012] Typically, the semiconductor is disposed on the surface of
said porous dielectric scaffold material. Thus, usually, the
semiconductor is disposed on the surfaces of pores within said
dielectric scaffold material.
[0013] In one embodiment, the optoelectronic device of the
invention as defined above is an optoelectronic device which
comprises a photoactive layer, wherein the photoactive layer
comprises:
[0014] said porous dielectric scaffold material; and
[0015] said semiconductor.
[0016] The invention further provides the use, as a photoactive
material in an optoelectronic device, of: (i) a porous dielectric
scaffold material; and (ii) a semiconductor having a band gap of
less than or equal to 3.0 eV, in contact with the scaffold
material.
[0017] Further provided is the use of a layer comprising: (i) a
porous dielectric scaffold material; and (ii) a semiconductor
having a band gap of less than or equal to 3.0 eV, in contact with
the scaffold material; as a photoactive layer in an optoelectronic
device.
[0018] In another aspect, the invention provides a photoactive
layer for an optoelectronic device comprising (a) a porous
dielectric scaffold material; (b) a semiconductor having a band gap
of less than or equal to 3.0 eV, in contact with the scaffold
material; and (c) a charge transporting material.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 is a schematic diagram of a photovoltaic device
comprising a mixed-anion perovskite.
[0020] FIG. 2 is an isometric cross-section drawing of a generic
meso-superstructured solar cell: (1) metal cathode, (2)
hole-conducting material, mesoporous insulating metal oxide with
absorber and hole-conducting material (see FIG. 4 for
clarification), (3) transparent conducting metal oxide (anode), (4)
transparent substrate, (5) metal anode, (6) compact n-type metal
oxide.
[0021] FIG. 3 is a schematic showing cross-section of the `active
layer` of a generic nanostructured solar cell: (2(i)) light
sensitive absorber, (2(ii)) insulating metal oxide, metal cathode,
(6) compact n-type metal oxide, (7) hole-conducting material.
[0022] FIG. 4 shows the current-voltage characteristics under
simulated AM1.5G illumination of a device assembled in mesoporous
absorber structure with hole-conductor: F:SnO.sub.2/Compact
TiO.sub.2/Mesoporous
Al.sub.2O.sub.3/CH.sub.3NH.sub.3PbCl.sub.2I/Spiro OMeTAD/Ag. On the
graph the voltage in volts is plotted on the x-axis and the current
density in mAcm.sup.-2 is plotted on the y-axis.
[0023] FIG. 5 shows the UV-Vis absorbance spectra for a device
assembled in absorber-sensitised structure with hole-conductor:
F:SnO.sub.2/Compact TiO.sub.2/mesoporous
oxide/CH.sub.3NH.sub.3PbCl.sub.2I/Spiro OMeTAD sealed using surlyn
and epoxy with light soaking under simulated AM1.5G illumination
over time. On the graph wavelength in nm is plotted on the x-axis
and the absorbance in arbitrary units is plotted on the y-axis.
[0024] FIG. 6 shows the Incident Photon-to-Electron Conversion
Efficiency (IPCE) action spectra of a device assembled in
mesoporous absorber structure with hole-conductor:
F:SnO.sub.2/Compact TiO.sub.2/Mesoporous
Al.sub.2O.sub.3/CH.sub.3NH.sub.3PbCl.sub.2I/Spiro-OMeTAD/Ag. On the
graph the wavelength in nm is plotted on the x-axis and the IPCE in
plotted on the y-axis.
[0025] FIG. 7 is a graph of optical band gap on the x-axis against
the open-circuit voltage on the y-axis for the "best-in-class"
solar cells for most current solar technologies. All the data for
the GaAs, Si, CIGS, CdTe, nanocrystaline Si (ncSi), amorphous Si
(aSi), CZTSS organic photovoltaics (OPV) and dye-sensitized solar
cells (DSC) was taken from Green, M. A., K. Emery, et al. (2012).
"Solar cell efficiency tables version 39)." Progress in
Photovoltaics 20(1): 12-20. The optical band gap has been estimated
by taking the onset of the incident photon-to-electron conversion
efficiency, as described in [Barkhouse DAR, Gunawan O, Gokmen T,
Todorov T K, Mitzi D B. Device characteristics of a 10.1%
hydrazineprocessed Cu2ZnSn(Se,S)4 solar cell. Progress in
Photovoltaics: Research and Applications 2012; published online
DOI: 10.1002/pip.1160.]
[0026] FIG. 8 is an X-ray diffraction pattern extracted at room
temperature from CH.sub.3NH.sub.3PbCl.sub.2I thin film coated onto
glass slide by using X'pert Pro X-ray Diffractometer. #
[0027] FIG. 9 shows a cross sectional SEM image of a complete
photoactive layer; Glass-FTO-mesoporous
Al2O3-K330-spiro-OMeTAD.
[0028] FIG. 10(a) shows UV-vis absorption spectra of the range of
FOPbI.sub.3yBr.sub.3(1-y) perovskites and FIG. 10(b) shows
steady-state photoluminescence spectra of the same samples.
[0029] FIG. 11(a-c) provides schematic diagrams of: (a) the general
perovskite ABX.sub.3 unit cell; (b) the cubic perovskite lattice
structure (the unit cell is shown as an overlaid square); and (c)
the tetragonal perovskite lattice structure arising from a
distortion of the BX.sub.6 octahedra (the unit cell is shown as the
larger overlaid square, and the pseudocubic unit cell that it can
be described by is shown as the smaller overlaid square).
[0030] FIG. 11(d) shows X-ray diffraction data for the
FOPbI.sub.3yBr.sub.3(1-y) perovskites, for various values of y
ranging from 0 to 1. FIG. 11(e) shows a magnification of the
transition between the (100) cubic peak and the (110) tetragonal
peak, corresponding to the (100) pseudocubic peak, as the system
moves from bromide to iodide. FIG. 11(f) shows a plot of bandgap
against calculated pseudocubic lattice parameter.
[0031] FIG. 12(a) shows average current-voltage characteristics for
a batch of solar cells comprising FOPbI.sub.3yBr.sub.3(1-y)
perovskites sensitizing mesoporous titania, with spiro-OMeTAD as
the hole transporter, measured under simulated AM1.5 sunlight. FIG.
12(b) shows a normalised external quantum efficiency for
representative cells, and FIG. 12(c) shows a plot of the device
parameters of merit for the batch, as a function of the iodine
fraction, y, in the FOPbI.sub.3yBr.sub.3(1-y) perovskite.
[0032] FIG. 13 shows plots of device parameters of merit for (i) a
meso-superstructured solar cell device (mesocrystal or MSSC), (ii)
a TiO.sub.2 nanoparticle device and (iii) an alumina device.
[0033] FIG. 14 shows the characteristic current voltage of the
three device types shown in FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0034] The invention provides an optoelectronic device comprising:
(i) a porous dielectric scaffold material; and (ii) a semiconductor
having a band gap of less than or equal to 3.0 eV, in contact with
the scaffold material.
[0035] As used herein, the term "porous" refers to a material
within which pores are arranged. In a "porous dielectric scaffold
material" the pores are volumes within the dielectric scaffold
where there is no dielectric scaffold material. The individual
pores may be the same size or different sizes. The size of the
pores is defined as the "pore size". For spherical pores, the pore
size is equal to the diameter of the sphere. For pores that are not
spherical, the pore size is equal to the diameter of a sphere, the
volume of said sphere being equal to the volume of the
non-spherical pore.
[0036] The term "dielectric material", as used herein, refers to
material which is an electrical insulator or a very poor conductor
of electric current. The term dielectric therefore excludes
semiconducting materials such as titania. The term dielectric, as
used herein, typically refers to materials having a band gap of
equal to or greater than 4.0 eV. (The band gap of titania is about
3.2 eV.)
[0037] The term "porous dielectric scaffold material", as used
herein, therefore refers to a dielectric material which is itself
porous, and which is capable of acting as a support for a further
material such as said coating comprising said perovskite.
[0038] The term "semiconductor" as used herein refers to a material
with electrical conductivity intermediate in magnitude between that
of a conductor and a dielectric. The semiconductor may be an n-type
semiconductor, a p-type semiconductor or an intrinsic
semiconductor. As used herein, the term "n-type", refers to an
n-type, or electron transporting material. The n-type semiconductor
used in the present invention may be any suitable n-type
semiconductor. As used herein, the term "p-type", refers to a
p-type, or hole transporting material. The p-type semiconductor
used in the present invention may be any suitable p-type
semiconductor. The intrinsic semiconductor used in the present
invention may be any suitable intrinsic semiconductor.
[0039] Any suitable semiconductor can be used in the optoelectronic
device of the invention. For instance, the semiconductor may be a
compound or elemental semiconductor comprising any element in the
periodic table or any combination of elements in the periodic
table. Examples of semiconductors which can be used in the
optoelectronic device of the invention include perovskites; and
compounds comprising gallium, niobium, tantalum, tungsten, indium,
neodinium, palladium, copper or lead, for instance, a chalcogenides
of antimony, copper, zinc, iron, or bismuth (such as copper
sulphide, iron sulphide, iron pyrite); copper zinc tin
chalcogenides, for example, copper zinc tin sulphides such a
Cu.sub.2ZnSnS.sub.4 (CZTS) and copper zinc tin sulphur-selenides
such as Cu.sub.2ZnSn(S.sub.1-xSe.sub.x).sub.4 (CZTSSe); copper
indium chalcogenides such as copper indium selenide (CIS); copper
indium gallium chalcogenides such as copper indium gallium
selenides (CuIn.sub.1-xGa.sub.xSe.sub.2) (CIGS); and copper indium
gallium diselenide. Further examples are group IV compound
semiconductors; group III-V semiconductors (e.g. gallium arsenide);
group II-VI semiconductors (e.g. cadmium selenide); group I-VII
semiconductors (e.g. cuprous chloride); group IV-VI semiconductors
(e.g. lead selenide); group V-VI semiconductors (e.g. bismuth
telluride); and group II-V semiconductors (e.g. cadmium
arsenide).
[0040] The skilled person is readily able to measure the band gap
of a semiconductor, by using well-known procedures which do not
require undue experimentation. For instance, the band gap of the
semiconductor can be estimated by constructing a photovoltaic diode
or solar cell from the semiconductor and determining the
photovoltaic action spectrum. The monochromatic photon energy at
which the photocurrent starts to be generated by the diode can be
taken as the band gap of the semiconductor; such a method was used
by Barkhouse et al., Prog. Photovolt: Res. Appl. 2012; 20:6-11.
References herein to the band gap of the semiconductor mean the
band gap as measured by this method, i.e. the band gap as
determined by recording the photovoltaic action spectrum of a
photovoltaic diode or solar cell constructed from the semiconductor
and observing the monochromatic photon energy at which significant
photocurrent starts to be generated.
[0041] In some embodiments, the band gap of the semiconductor is
less than or equal to 2.5 eV. The band gap may for instance be less
than or equal to 2.3 eV, or for instance less than or equal to 2.0
eV.
[0042] Usually, the band gap is at least 0.5 eV. However, other
embodiments are also envisaged, in which the band gap of the
semiconductor is close to 0, so that the semiconductor has
conducting properties similar to those of a metal. Thus, the band
gap of the semiconductor may be from 0.5 eV to 3.0 eV, or for
instance from 0.5 eV to 2.8 eV. In some embodiments it is from 0.5
eV to 2.5 eV, or for example from 0.5 eV to 2.3 eV. The band gap of
the semiconductor may for instance be from 0.5 eV to 2.0 eV. In
other embodiments, the band gap of the semiconductor may be from
1.0 eV to 3.0 eV, or for instance from 1.0 eV to 2.8 eV. In some
embodiments it is from 1.0 eV to 2.5 eV, or for example from 1.0 eV
to 2.3 eV. The band gap of the semiconductor may for instance be
from 1.0 eV to 2.0 eV.
[0043] The band gap of the semiconductor can be from 1.2 eV to 1.8
eV. The band gaps of organometal halide perovskite semiconductors,
for example, are typically in this range and may for instance, be
about 1.5 eV or about 1.6 eV. Thus, in one embodiment the band gap
of the semiconductor is from 1.3 eV to 1.7 eV.
[0044] The semiconductor is in contact with the porous dielectric
scaffold material, i.e. it is supported by the scaffold material.
Thus, the semiconductor is typically disposed on the surface of the
porous dielectric scaffold material, like a coating. Thus, as the
skilled person will appreciate, this means that the semiconductor
is usually coated on the inside surfaces of pores within the porous
dielectric scaffold material, as well as on the outer surfaces of
the scaffold material. This is shown schematically in FIG. 1. If
the semiconductor is in contact with the scaffold material within
the pores of the scaffold material, the pores are usually not
completely filled by the semiconductor. Rather, the semiconductor
is typically present as a coating on the inside surface of the
pores.
[0045] Thus, typically the semiconductor is disposed on the surface
of the porous dielectric scaffold material. Usually, the
semiconductor is disposed on the surfaces of pores within the
scaffold.
[0046] Typically, in the optoelectronic device of the invention the
semiconductor is disposed on the surface of said porous dielectric
scaffold material. Thus, as explained above, the semiconductor may
be disposed on the surface of pores within said dielectric scaffold
material. As the skilled person will appreciate, the semiconductor
may be disposed on the surfaces of some or all pores within said
dielectric scaffold material.
[0047] Usually, in the optoelectronic device of the invention, the
dielectric scaffold material comprises an oxide of aluminium,
germanium, zirconium, silicon, yttrium or ytterbium, or mixtures
thereof, for instance, the dielectric scaffold material may
comprise an oxide of aluminium, germanium, zirconium, silicon,
yttrium or ytterbium; or alumina silicate. More typically, the
dielectric scaffold material comprises porous alumina.
[0048] Typically, in the optoelectronic device of the invention,
the dielectric scaffold material is mesoporous.
[0049] The term "mesoporous", as used herein means that the pores
in the porous structure are microscopic and have a size which is
usefully measured in nanometres (nm). The mean pore size of the
pores within a "mesoporous" structure may for instance be anywhere
in the range of from 1 nm to 100 nm, or for instance from 2 nm to
50 nm. Individual pores may be different sizes and may be any
shape.
[0050] Typically, in the optoelectronic device of the invention,
the dielectric scaffold material comprises mesoporous alumina.
[0051] The porosity of said dielectric scaffold material is usually
at least 50%. For instance, the porosity may be about 70%. In one
embodiment, the porosity is at least 60%, for instance at least
70%.
[0052] As defined above, a porous material is material within which
pores are arranged. The total volume of the porous material is the
volume of the material plus the volume of the pores. The term
"porosity", as used herein, is the percentage of the total volume
of the material that is occupied by the pores. Thus if, for
example, the total volume of the porous material was 100 nm.sup.3
and the volume of the pores was 70 nm.sup.3, the porosity of the
material would be equal to 70%.
[0053] Often, in the optoelectronic device of the invention, the
dielectric scaffold material, is mesoporous.
[0054] Typically, the semiconductor used in the present invention
is also a photosensitizing material, i.e. a material which is
capable of performing both photogeneration and charge (electron)
transportation.
[0055] In the optoelectronic device of the invention, the
semiconductor may comprise a copper zinc tin chalcogenide, for
example, a copper zinc tin sulphide such a Cu.sub.2ZnSnS.sub.4
(CZTS) and copper zinc tin sulphur-selenides such as
Cu.sub.2ZnSn(S.sub.1-xSe.sub.x).sub.4 (CZTSSe).
[0056] Alternatively, the semiconductor may comprise an antimony or
bismuth chalcogenide, such as, for example, Sb.sub.2S.sub.3,
Sb.sub.2Se.sub.3, Bi.sub.2S.sub.3 or Bi.sub.2Se.sub.3.
[0057] The semiconductor may, for instance, comprise antimony
sulphide.
[0058] The semiconductor may alternatively be gallium arsenide.
[0059] Usually, the semiconductor comprises a perovskite as herein
defined.
[0060] In one embodiment, in the optoelectronic device of the
invention, the semiconductor is an n-type semiconductor.
[0061] Usually, in the optoelectronic device of the invention, the
semiconductor comprises an n-type semiconductor comprising a
perovskite.
[0062] In one embodiment, in the optoelectronic device of the
invention, semiconductor comprises a perovskite, Sb.sub.2S.sub.3,
Sb.sub.2Se.sub.3, Bi.sub.2S.sub.3, Bi.sub.2Se.sub.3, CIS, CIGS,
CZTS, CZTSSe, FeS.sub.2, CdS, CdSe, PbS, PbSe, Ge or GaAs,
preferably wherein the semiconductor comprises a perovskite, CZTS,
CZTSSe, gallium arsenide, an antimony chalcogenide, or a bismuth
chalcogenide.
[0063] The semiconductor may, for instance, comprise antimony
sulphide.
[0064] In one embodiment, in the optoelectronic device of the
invention, the semiconductor is a p-type semiconductor.
[0065] Often, the p-type semiconductor comprises a perovskite or a
chalcogenide.
[0066] In one embodiment, in the optoelectronic device of the
invention, the semiconductor is an intrinsic semiconductor.
[0067] Usually, the intrinsic semiconductor comprises a perovskite
or gallium aresenide.
[0068] In some embodiments, the semiconductor comprises an oxide of
gallium, niobium, tantalum, tungsten, indium, neodymium or
palladium, or a sulphide of zinc or cadmium, provided of course
that the semiconductor has a band gap of less than or equal to 3.0
eV.
[0069] Alternatively, in some embodiments, the semiconductor
comprises an oxide of nickel, vanadium, lead, copper or molybdenum,
provided of course that the semiconductor has a band gap of less
than or equal to 3.0 eV.
[0070] In one embodiment, in the optoelectronic device of the
invention, the semiconductor comprises a perovskite,
Sb.sub.2S.sub.3, Sb.sub.2Se.sub.3, Bi.sub.2S.sub.3,
Bi.sub.2Se.sub.3, CIS, CIGS, CZTS, CZTSSe, FeS.sub.2, CdS, CdSe,
PbS, PbSe, Ge or GaAs, preferably wherein the semiconductor
comprises a perovskite, CZTS, CZTSSe, gallium arsenide, an antimony
chalcogenide, or a bismuth chalcogenide.
[0071] The semiconductor may, for instance, comprise antimony
sulphide.
[0072] Typically, in the optoelectronic device of the invention,
the semiconductor has a band gap of less than or equal to 2.5 eV,
optionally less than or equal to 2.0 eV.
[0073] Often, the band gap is at least 0.5 eV.
[0074] In some embodiments of the optoelectronic device of the
invention, the semiconductor comprises a perovskite.
[0075] The term "perovskite", as used herein, refers to a material
with a three-dimensional crystal structure related to that of
CaTiO.sub.3 or a material comprising a layer of material, wherein
the layer has a structure related to that of CaTiO.sub.3. The
structure of CaTiO.sub.3 can be represented by the formula
ABX.sub.3, wherein A and B are cations of different sizes and X is
an anion. In the unit cell, the A cations are at (0,0,0), the B
cations are at (1/2, 1/2, 1/2) and the X anions are at (1/2, 1/2,
0). The A cation is usually larger than the B cation. The skilled
person will appreciate that when A, B and X are varied, the
different ion sizes may cause the structure of the perovskite
material to distort away from the structure adopted by CaTiO.sub.3
to a lower-symmetry distorted structure. The symmetry will also be
lower if the material comprises a layer that has a structure
related to that of CaTiO.sub.3. Materials comprising a layer of
perovskite material are well known. For instance, the structure of
materials adopting the K.sub.2NiF.sub.4-type structure comprises a
layer of perovskite material. The skilled person will appreciate
that a perovskite material can be represented by the formula
[A][B][X].sub.3, wherein [A] is at least one cation, [B] is at
least one cation and [X] is at least one anion. When the perovskite
comprise more than one A cation, the different A cations may
distributed over the A sites in an ordered or disordered way. When
the perovskite comprise more than one B cation, the different B
cations may distributed over the B sites in an ordered or
disordered way. When the perovskite comprise more than one X anion,
the different X anions may distributed over the X sites in an
ordered or disordered way. The symmetry of a perovskite comprising
more than one A cation, more than one B cation or more than one X
cation, will be lower than that of CaTiO.sub.3.
[0076] As the skilled person will appreciate, the perovskite may be
a perovskite which acts as an n-type, electron-transporting
semiconductor when photo-doped. Alternatively, it may be a
perovskite which acts as a p-type hole-transporting semiconductor
when photo-doped. Thus, the perovksite may be n-type or p-type, or
it may be an intrinsic semiconductor. Typically, the perovskite
employed is one which acts as an n-type, electron-transporting
semiconductor when photo-doped.
[0077] The optoelectronic device of the invention usually further
comprises a charge transporting material disposed within pores of
said porous material. The charge transporting material may be a
hole transporting material or an electron transporting material. As
the skilled person will appreciate, when the perovskite is an
intrinsic semiconductor the charge transporting material can be a
hole transporting material or an electron transporting material.
However, when the perovskite is an n-type semiconductor, the charge
transporting material is typically a hole transporting material.
Also, when the perovskite is a p-type semiconductor, the charge
transporting material is typically an electron transporting
material.
[0078] Usually, in the optoelectronic device of the invention, the
perovskite comprises at least one anion selected from halide anions
and chalcogenide anions.
[0079] The term "halide" refers to an anion of a group 7 element,
i.e., of a halogen. Typically, halide refers to a fluoride anion, a
chloride anion, a bromide anion, an iodide anion or an astatide
anion.
[0080] The term "chalcogenide anion", as used herein refers to an
anion of group 6 element, i.e. of a chalcogen. Typically,
chalcogenide refers to an oxide anion, a sulphide anion, a selenide
anion or a telluride anion.
[0081] In the optoelectronic device of the invention, the
perovskite often comprises a first cation, a second cation, and
said at least one anion.
[0082] As the skilled person will appreciate, the perovskite may
comprise further cations or further anions. For instance, the
perovskite may comprise two, three or four different first cations;
two, three or four different second cations; or two, three of four
different anions.
[0083] Typically, in the optoelectronic device of the invention,
the second cation in the perovskite is a metal cation. More
typically, the second cation is a divalent metal cation. For
instance, the second cation may be selected from Ca.sup.2+,
Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+,
Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+,
Yb.sup.2+ and Eu.sup.2+. Usually, the second cation is selected
from Sn.sup.2+ and Pb.sup.2+.
[0084] In the optoelectronic device of the invention, the first
cation in the perovskite is usually an organic cation.
[0085] The term "organic cation" refers to a cation comprising
carbon. The cation may comprise further elements, for example, the
cation may comprise hydrogen, nitrogen or oxygen.
[0086] Usually, in the optoelectronic device of the invention, the
organic cation has the formula
(R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+, wherein:
[0087] R.sub.1 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
[0088] R.sub.2 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
[0089] R.sub.3 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
and
[0090] R.sub.4 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl.
[0091] As used herein, an alkyl group can be a substituted or
unsubstituted, linear or branched chain saturated radical, it is
often a substituted or an unsubstituted linear chain saturated
radical, more often an unsubstituted linear chain saturated
radical. A C.sub.1-C.sub.20 alkyl group is an unsubstituted or
substituted, straight or branched chain saturated hydrocarbon
radical having from 1 to 20 carbon atoms. Typically it is
C.sub.1-C.sub.10 alkyl, for example methyl, ethyl, propyl, butyl,
pentyl, hexyl, heptyl, octyl, nonyl or decyl, or C.sub.1-C.sub.6
alkyl, for example methyl, ethyl, propyl, butyl, pentyl or hexyl,
or C.sub.1-C.sub.4 alkyl, for example methyl, ethyl, i-propyl,
n-propyl, t-butyl, s-butyl or n-butyl.
[0092] When an alkyl group is substituted it typically bears one or
more substituents selected from substituted or unsubstituted
C.sub.1-C.sub.20 alkyl, substituted or unsubstituted aryl (as
defined herein), cyano, amino, C.sub.1-C.sub.10 alkylamino,
di(C.sub.1-C.sub.10)alkylamino, arylamino, diarylamino,
arylalkylamino, amido, acylamido, hydroxy, oxo, halo, carboxy,
ester, acyl, acyloxy, C.sub.1-C.sub.20 alkoxy, aryloxy, haloalkyl,
sulfonic acid, sulfhydryl (i.e. thiol, --SH), C.sub.1-C.sub.10
alkylthio, arylthio, sulfonyl, phosphoric acid, phosphate ester,
phosphonic acid and phosphonate ester. Examples of substituted
alkyl groups include haloalkyl, hydroxyalkyl, aminoalkyl,
alkoxyalkyl and alkaryl groups. The term alkaryl, as used herein,
pertains to a C.sub.1-C.sub.20 alkyl group in which at least one
hydrogen atom has been replaced with an aryl group. Examples of
such groups include, but are not limited to, benzyl (phenylmethyl,
PhCH.sub.2--), benzhydryl (Ph.sub.2CH--), trityl (triphenylmethyl,
Ph.sub.3C--), phenethyl (phenylethyl, Ph-CH.sub.2CH.sub.2--),
styryl (Ph-CH.dbd.CH--), cinnamyl (Ph-CH.dbd.CH--CH.sub.2--).
[0093] Typically a substituted alkyl group carries 1, 2 or 3
substituents, for instance 1 or 2.
[0094] An aryl group is a substituted or unsubstituted, monocyclic
or bicyclic aromatic group which typically contains from 6 to 14
carbon atoms, preferably from 6 to 10 carbon atoms in the ring
portion. Examples include phenyl, naphthyl, indenyl and indanyl
groups. An aryl group is unsubstituted or substituted. When an aryl
group as defined above is substituted it typically bears one or
more substituents selected from C.sub.1-C.sub.6 alkyl which is
unsubstituted (to form an aralkyl group), aryl which is
unsubstituted, cyano, amino, C.sub.1-C.sub.10 alkylamino,
di(C.sub.1-C.sub.10)alkylamino, arylamino, diarylamino,
arylalkylamino, amido, acylamido, hydroxy, halo, carboxy, ester,
acyl, acyloxy, C.sub.1-C.sub.20 alkoxy, aryloxy, haloalkyl,
sulfhydryl (i.e. thiol, --SH), C.sub.1-10 alkylthio, arylthio,
sulfonic acid, phosphoric acid, phosphate ester, phosphonic acid
and phosphonate ester and sulfonyl. Typically it carries 0, 1, 2 or
3 substituents. A substituted aryl group may be substituted in two
positions with a single C.sub.1-C.sub.6 alkylene group, or with a
bidentate group represented by the formula
--X--(C.sub.1-C.sub.6)alkylene, or
--X--(C.sub.1-C.sub.6)alkylene-X--, wherein X is selected from O, S
and NR, and wherein R is H, aryl or C.sub.1-C.sub.6 alkyl. Thus a
substituted aryl group may be an aryl group fused with a cycloalkyl
group or with a heterocyclyl group. The ring atoms of an aryl group
may include one or more heteroatoms (as in a heteroaryl group).
Such an aryl group (a heteroaryl group) is a substituted or
unsubstituted mono- or bicyclic heteroaromatic group which
typically contains from 6 to 10 atoms in the ring portion including
one or more heteroatoms. It is generally a 5- or 6-membered ring,
containing at least one heteroatom selected from O, S, N, P, Se and
Si. It may contain, for example, 1, 2 or 3 heteroatoms. Examples of
heteroaryl groups include pyridyl, pyrazinyl, pyrimidinyl,
pyridazinyl, furanyl, thienyl, pyrazolidinyl, pyrrolyl, oxazolyl,
oxadiazolyl, isoxazolyl, thiadiazolyl, thiazolyl, isothiazolyl,
imidazolyl, pyrazolyl, quinolyl and isoquinolyl. A heteroaryl group
may be unsubstituted or substituted, for instance, as specified
above for aryl. Typically it carries 0, 1, 2 or 3 substituents.
[0095] Mainly, in the optoelectronic device of the invention,
R.sub.1 in the organic cation is hydrogen, methyl or ethyl, R.sub.2
is hydrogen, methyl or ethyl, R.sub.3 is hydrogen, methyl or ethyl,
and R.sub.4 is hydrogen, methyl or ethyl. For instance R.sub.1 may
be hydrogen or methyl, R.sub.2 may be hydrogen or methyl, R.sub.3
may be hydrogen or methyl, and R.sub.4 may be hydrogen or
methyl.
[0096] Alternatively, the organic cation may have the formula
(R.sub.5NH.sub.3).sup.+, wherein: R.sub.5 is hydrogen, or
unsubstituted or substituted C.sub.1-C.sub.20 alkyl. For instance,
R.sub.5 may be methyl or ethyl. Typically, R.sub.5 is methyl.
[0097] In some embodiments, the organic cation has the formula
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, wherein: R.sub.5
is hydrogen, unsubstituted or substituted C.sub.1-C.sub.20 alkyl,
or unsubstituted or substituted aryl; R.sub.6 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; R.sub.7 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; and R.sub.8 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl.
[0098] Typically, R.sub.5 in the organic cation is hydrogen, methyl
or ethyl, R.sub.6 is hydrogen, methyl or ethyl, R.sub.7 is
hydrogen, methyl or ethyl, and R.sub.8 is hydrogen, methyl or
ethyl. For instance R.sub.5 may be hydrogen or methyl, R.sub.6 may
be hydrogen or methyl, R.sub.7 may be hydrogen or methyl, and
R.sub.8 may be hydrogen or methyl.
[0099] The organic cation may, for example, have the formula
(H.sub.2N.dbd.CH--NH.sub.2)+.
[0100] In one embodiment, the perovskite is a mixed-anion
perovskite comprising a first cation, a second cation, and two or
more different anions selected from halide anions and chalcogenide
anions. For instance, the mixed-anion perovskite may comprise two
different anions and, for instance, the anions may be a halide
anion and a chalcogenide anion, two different halide anions or two
different chalcogenide anions. The first and second cations may be
as further defined hereinbefore. Thus the first cation may be an
organic cation, which may be as further defined herein. For
instance it may be a cation of formula
(R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+, or formula
(R.sub.5NH.sub.3).sup.+, as defined above. The second cation may be
a divalent metal cation. For instance, the second cation may be
selected from Ca.sup.2+, Sr.sup.2+, Cd.sup.2+, Cu.sup.2+,
Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Pd.sup.2+, Ge.sup.2+,
Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+ and Eu.sup.2+. Usually,
the second cation is selected from Sn.sup.2+ and Pb.sup.2+.
[0101] In another embodiment, the perovskite is a mixed-anion
perovskite comprising a first cation, a second cation, and two or
more different anions selected from halide anions and chalcogenide
anions. For instance, the mixed-anion perovskite may comprise two
different anions and, for instance, the anions may be a halide
anion and a chalcogenide anion, two different halide anions or two
different chalcogenide anions. The first and second cations may be
as further defined hereinbefore. Thus the first cation may be an
organic cation, which may be as further defined herein. For
instance it may be a cation of formula
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, or formula
((H.sub.2N.dbd.CH--NH.sub.2).sup.+, as defined above. The second
cation may be a divalent metal cation. For instance, the second
cation may be selected from Ca.sup.2+, Sr.sup.2+, Cd.sup.2+,
Cd.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Pd.sup.2+,
Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+ and
Eu.sup.2+. Usually, the second cation is selected from Sn.sup.2+
and Pb.sup.2+.
[0102] In the optoelectronic device of the invention, the
perovskite is usually a mixed-halide perovskite, wherein said two
or more different anions are two or more different halide anions.
Typically, they are two or three halide anions, more typically, two
different halide anions. Usually the halide anions are selected
from fluoride, chloride, bromide and iodide, for instance chloride,
bromide and iodide.
[0103] Often, in the optoelectronic device of the invention, the
perovskite is a perovskite compound of the formula (I):
[A][B][X].sub.3 (I)
wherein:
[0104] [A] is at least one organic cation;
[0105] [B] is at least one metal cation; and
[0106] [X] is said at least one anion.
[0107] For instance, the perovskite of the formula (I) may comprise
one, two, three or four different metal cations, typically one or
two different metal cations. The perovskite of the formula (I),
may, for instance, comprise one, two, three or four different
organic cations, typically one or two different organic cations.
The perovskite of the formula (I), may, for instance, comprise one
two, three or four different anions, typically two or three
different anions.
[0108] The organic and metal cations may be as further defined
hereinbefore. Thus the organic cations may be selected from cations
of formula (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+ and cations of
formula (R.sub.5NH.sub.3).sup.+, as defined above. The metal
cations may be selected from divalent metal cations. For instance,
the metal cations may be selected from Ca.sup.2+, Sr.sup.2+,
Cd.sup.2+, Cd.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+,
Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+
and Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or
Pb.sup.2+.
[0109] The organic cation may, for instance, be selected from
cations of formula (R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+,
and cations of formula ((H.sub.2N.dbd.CH--NH.sub.2).sup.+. The
metal cations may be selected from divalent metal cations. For
instance, the metal cations may be selected from Ca.sup.2+,
Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+,
Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+,
Yb.sup.2+ and Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or
Pb.sup.2+.
[0110] Typically, in the optoelectronic device of the invention,
[X] in formula (I) is two or more different anions selected from
halide anions and chalcogenide anions. More typically, [X] is two
or more different halide anions.
[0111] In one embodiment, the perovskite is a perovskite compound
of the formula (IA):
AB[X].sub.3 (IA)
wherein:
[0112] A is an organic cation;
[0113] B is a metal cation; and
[0114] [X] is at least one anion.
[0115] Often, in the optoelectronic device of the invention, [X] in
formula (IA) is two or more different anions selected from halide
anions and chalcogenide anions. Usually, [X] is two or more
different halide anions. Preferably, [X] is two or three different
halide anions. More preferably, [X] is two different halide anions.
In another embodiment [X] is three different halide anions.
[0116] The organic and metal cations may be as further defined
hereinbefore. Thus the organic cation may be selected from cations
of formula (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+ and cations of
formula (R.sub.5NH.sub.3).sup.+, as defined above. The metal cation
may be a divalent metal cation. For instance, the metal cation may
be selected from Ca.sup.2+, Sr.sup.2+, Cd.sup.2+, Cu.sup.2+,
Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Pd.sup.2+, Ge.sup.2+,
Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+ and Eu.sup.2+. Usually,
the metal cation is Sn.sup.2+ or Pb.sup.2+.
[0117] The organic cation may, for instance, be selected from
cations of formula (R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+,
and cations of formula (H.sub.2N.dbd.CH--NH.sub.2).sup.+, as
defined above. The metal cation may be a divalent metal cation. For
instance, the metal cation may be selected from Ca.sup.2+,
Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+,
Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+,
Yb.sup.2+ and Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or
Pb.sup.2+.
[0118] Typically, in the optoelectronic device of the invention,
the perovskite is a perovskite compound of formula (II):
ABX.sub.3-yX'.sub.y (II)
wherein:
[0119] A is an organic cation;
[0120] B is a metal cation;
[0121] X is a first halide anion;
[0122] X' is a second halide anion which is different from the
first halide anion; and
[0123] y is from 0.05 to 2.95.
[0124] Usually, y is from 0.5 to 2.5, for instance from 0.75 to
2.25. Typically, y is from 1 to 2.
[0125] Again, the organic and metal cations may be as further
defined hereinbefore. Thus the organic cation may be a cation of
formula (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+ or, more typically, a
cation of formula (R.sub.5NH.sub.3).sup.+, as defined above. The
metal cation may be a divalent metal cation. For instance, the
metal cation may be selected from Ca.sup.2+, Sr.sup.2+, Cd.sup.2+,
Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Pd.sup.2+,
Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+ and
Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or Pb.sup.2+.
[0126] In some embodiments, the perovskite is a perovskite compound
of formula (IIa):
ABX.sub.3zX'.sub.3(1-z) (IIa)
wherein:
[0127] A is an organic cation of the formula
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, wherein: R.sub.5
is hydrogen, unsubstituted or substituted C.sub.1-C.sub.20 alkyl,
or unsubstituted or substituted aryl; R.sub.6 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; R.sub.7 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; and R.sub.8 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl;
[0128] B is a metal cation;
[0129] X is a first halide anion;
[0130] X' is a second halide anion which is different from the
first halide anion; and z is greater than 0 and less than 1.
[0131] Usually, z is from 0.05 to 0.95.
[0132] Preferably, z is from 0.1 to 0.9. z may, for instance, be
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, or z may be a range
of from any one of these values, to any other of these values (for
instance from 0.2 to 0.7, or from 0.1 to 0.8).
[0133] Typically, X is a halide anion and X' is a chalcogenide
anion, or X and X' are two different halide anions or two different
chalcogenide anions. Usually, X and X' are two different halide
anions. For instance, one of said two or more different halide
anions may be iodide and another of said two or more different
halide anions may be bromide.
[0134] Usually, B is a divalent metal cation. For instance, B may
be a divalent metal cation, selected from Ca.sup.2+, Sr.sup.2+,
Cd.sup.2+, Co.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+,
Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+
and Eu.sup.2+. Usually, B is a divalent metal cation selected from
Sn.sup.2+ and Pb.sup.2+. For instance, B may be Pb.sup.2+.
[0135] The organic cation may, for instance, be
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, wherein: R.sub.5,
R.sub.6, R.sub.7 and R.sub.8 are independently selected from
hydrogen and unsubstituted or substituted C.sub.1-C.sub.6 alkyl.
For instance, the organic cation may be
(H.sub.2N.dbd.CH--NH.sub.2).sup.+.
[0136] Often, in the optoelectronic device of the invention, the
perovskites are selected from CH.sub.3NH.sub.3PbI.sub.3,
CH.sub.3NH.sub.3PbBr.sub.3, CH.sub.3NH.sub.3PbCl.sub.3,
CH.sub.3NH.sub.3PbF.sub.3, CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3SnBrI.sub.2,
CH.sub.3NH.sub.3SnBrCl.sub.2, CH.sub.3NH.sub.3SnF.sub.2Br,
CH.sub.3NH.sub.3SnIBr.sub.2, CH.sub.3NH.sub.3SnICl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2I, CH.sub.3NH.sub.3SnClBr.sub.2,
CH.sub.3NH.sub.3SnI.sub.2Cl and CH.sub.3NH.sub.3SnF.sub.2Cl. For
instance, in the optoelectronic device of the invention, the
perovskites may be selected from CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3SnBrI.sub.2,
CH.sub.3NH.sub.3SnBrCl.sub.2, CH.sub.3NH.sub.3SnF.sub.2Br,
CH.sub.3NH.sub.3SnIBr.sub.2, CH.sub.3NH.sub.3SnICl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2I, CH.sub.3NH.sub.3SnClBr.sub.2,
CH.sub.3NH.sub.3SnI.sub.2Cl and CH.sub.3NH.sub.3SnF.sub.2Cl.
Typically, the perovskite is selected from
CH.sub.3NH.sub.3PbBrI.sub.2, CH.sub.3NH.sub.3PbBrCl.sub.2,
CH.sub.3NH.sub.3PbIBr.sub.2, CH.sub.3NH.sub.3PbICl.sub.2,
CH.sub.3NH.sub.3PbClBr.sub.2, CH.sub.3NH.sub.3PbI.sub.2Cl,
CH.sub.3NH.sub.3 SnF.sub.2Br, CH.sub.3NH.sub.3 SnICl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2I, CH.sub.3NH.sub.3SnI.sub.2Cl and
CH.sub.3NH.sub.3SnF.sub.2Cl. More typically, the perovskite is
selected from CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3 SnF.sub.2Br,
CH.sub.3NH.sub.3 SnF.sub.2I and CH.sub.3NH.sub.3 SnF.sub.2Cl.
Usually, the perovskite is selected from
CH.sub.3NH.sub.3PbBrI.sub.2, CH.sub.3NH.sub.3PbBrCl.sub.2,
CH.sub.3NH.sub.3PbIBr.sub.2, CH.sub.3NH.sub.3PbICl.sub.2,
CH.sub.3NH.sub.3 SnF.sub.2Br, and CH.sub.3NH.sub.3 SnF.sub.2I.
[0137] In some embodiments, the perovskite may be a perovskite of
formula (H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3zBr.sub.3(1-z), wherein
z is greater than 0 or less than 1. z may be as further defined
herein.
[0138] The optoelectronic device of the invention may comprise said
perovskite and a single-anion perovskite, wherein said single anion
perovskite comprises a first cation, a second cation and an anion
selected from halide anions and chalcogenide anions; wherein the
first and second cations are as herein defined for said mixed-anion
perovskite. For instance, the optoelectronic device may comprise:
CH.sub.3NH.sub.3PbICl.sub.2 and CH.sub.3NH.sub.3PbI.sub.3;
CH.sub.3NH.sub.3PbICl.sub.2 and CH.sub.3NH.sub.3PbBr.sub.3;
CH.sub.3NH.sub.3PbBrCl.sub.2 and CH.sub.3NH.sub.3PbI.sub.3; or
CH.sub.3NH.sub.3PbBrCl.sub.2 and CH.sub.3NH.sub.3PbBr.sub.3.
[0139] The optoelectronic device may comprise a perovskite of
formula (H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3zBr.sub.3(1-z), wherein
z is as defined herein, and a single-anion perovskite such as
(H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3 or
(H.sub.2N.dbd.CH--NH.sub.2)PbBr.sub.3.
[0140] Alternatively, the optoelectronic device of the invention
may comprise more than one perovskite, wherein each perovskite is a
mixed-anion perovskite, and wherein said mixed-anion perovskite is
as herein defined. For instance, the optoelectronic device may
comprise two or three said perovskites. The optoelectronic device
of the invention may, for instance, comprise two perovskites
wherein both perovskites are mixed-anion perovskites. For instance,
the optoelectronic device may comprise: CH.sub.3NH.sub.3PbICl.sub.2
and CH.sub.3NH.sub.3PbIBr.sub.2; CH.sub.3NH.sub.3PbICl.sub.2 and
CH.sub.3NH.sub.3PbBrI.sub.2; CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbIBr.sub.2; or CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbIBr.sub.2.
[0141] The optoelectronic device may comprise two different
perovskites, wherein each perovskite is a perovskite of formula
(H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3zBr.sub.3(1-z), wherein z is as
defined herein.
[0142] In some embodiments of the optoelectronic device of the
invention, when [B] is a single metal cation which is Pb.sup.2+,
one of said two or more different halide anions is iodide or
fluoride; and when [B] is a single metal cation which is Sn.sup.2+
one of said two or more different halide anions is fluoride.
Usually, in some embodiments of the optoelectronic device of the
invention, one of said two or more different halide anions is
iodide or fluoride. Typically, in some embodiments of the
optoelectronic device of the invention, one of said two or more
different halide anions is iodide and another of said two or more
different halide anions is fluoride or chloride. Often, in some
embodiments of the optoelectronic device of the invention, one of
said two or more different halide anions is fluoride. Typically, in
some embodiments of the optoelectronic device of the invention,
either: (a) one of said two or more different anions is fluoride
and another of said said two or more different anions is chloride,
bromide or iodide; or (b) one of said two or more different anions
is iodide and another of said two or more different anions is
fluoride or chloride. Typically, [X] is two different halide anions
X and X'. Often, in the optoelectronic device of the invention,
said divalent metal cation is Sn.sup.2+. Alternatively, in the
optoelectronic device of the invention, said divalent metal cation
may be Pb.sup.2+.
[0143] Usually, the optoelectronic device of the invention
comprises a layer comprising said porous dielectric scaffold
material and said semiconductor.
[0144] Typically, the photoactive layer comprises: said porous
dielectric scaffold material; and said semiconductor.
[0145] In one embodiment, the optoelectronic device of the
invention further comprises a charge transporting material.
[0146] The charge transporting material may, for instance, be a
hole transporting material or an electron transporting
material.
[0147] When the charge transporting material is an hole
transporting material, the hole transporting material in the
optoelectronic device of the invention may be any suitable p-type
or hole-transporting, semiconducting material. Typically, the hole
transporting material is a small molecular or polymer-based hole
conductor.
[0148] Typically, when the charge transporting material is an hole
transporting material, the charge transporting material is a solid
state hole transporting material or a liquid electrolyte.
[0149] Often, when the charge transporting material is an hole
transporting material, the charge transporting material is a
polymeric or molecular hole transporter. Typically, the charge
transporting material comprises spiro-OMeTAD
(2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene)),
P3HT (poly(3-hexylthiophene)), PCPDTBT
(Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta-
[2,1-b:3,4-b']dithiophene-2,6-diyl]]), PVK
(poly(N-vinylcarbazole)), HTM-TFSI (1-hexyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide), Li-TFSI (lithium
bis(trifluoromethanesulfonyl)imide) or tBP (tert-butylpyridine).
Usually, the charge transporting material is selected from
spiro-OMeTAD, P3HT, PCPDTBT and PVK. Preferable, the hole
transporting material is spiro-OMeTAD.
[0150] When the charge transporting material is an hole
transporting material, the charge transporting material may be a
molecular hole transporter, or a polymer or copolymers. Often, the
charge transporting material is a molecular hole transporting
material, a polymer or copolymer comprises one or more of the
following moieties: thiophenyl, phenelenyl, dithiazolyl,
benzothiazolyl, diketopyrrolopyrrolyl, ethoxydithiophenyl, amino,
triphenyl amino, carbozolyl, ethylene dioxythiophenyl,
dioxythiophenyl, or fluorenyl.
[0151] Alternatively, when the charge transporting material is an
hole transporting material, the charge transporting material may be
an inorganic hole transporter, for instance, the charge
transporting material may be CuI, CuBr, CuSCN, Cu.sub.2O, CuO or
CIS.
[0152] When the charge transporting material is an electron
transporting material, the charge transporting material often
comprises a fullerene or perylene, or derivatives thereof, or
P(NDI2OD-T2). For instance, the charge transporting material may be
P(NDI2OD-T2).
[0153] In some embodiments, the charge transporting material
comprises a perovskite.
[0154] When the charge transporting material is a hole transporting
material, the hole transporting material may comprise a
perovskite.
[0155] Likewise, when the charge transporting material is an
electron transporting material, the electron transporting material
may comprise a perovskite.
[0156] Usually, said semiconductor comprises a first perovskite,
wherein the first perovskite is as defined hereinabove, and said
charge transporting material comprises a second perovskite, wherein
the first and second perovskites are the same or different.
[0157] As described above, the semiconductor must have a band gap
of equal to or less than 3.0 eV. The skilled person will appreciate
that the second perovskite is not necessarily a perovskite that has
a band gap of equal to or less than 3.0 eV. Thus the second
perovskite may have a band gap of equal to or less than 3.0 eV or,
in some embodiments, the second perovskite may have a band gap of
greater than 3.0 eV.
[0158] The skilled person will also appreciate that, usually,
either (i) the first perovskite is an n-type material and the
second perovskite is a p-type material, or (ii) the first
perovskite is a p-type material and the second perovskite is an
n-type material. The skilled person will also appreciate that the
addition of a doping agent to a perovskite may be used to control
the charge transfer properties of that perovskite. Thus, for
instance, a perovskite that is an instrinic material may be doped
to form an n-type or a p-type material. Accordingly, the first
perovskite and/or the second perovskite may comprise one or more
doping agent. Typically the doping agent is a dopant element.
[0159] The addition of different doping agents to different samples
of the same material may result in the different samples having
different charge transfer properties. For instance, the addition of
one doping agent to a first sample of perovskite material may
result in the first sample becoming an n-type material, whilst the
addition of a different doping agent to a second sample of the same
perovskite material may result in the second sample becoming a
p-type material.
[0160] In some embodiments of the optoelectronic device of the
invention, the first and second perovskites may be the same.
[0161] Alternatively, the first and second perovskites may be
different. When the first and second perovskites are different, at
least one of the first and second perovskites may comprise a doping
agent. The first perovskite may for instance comprise a doping
agent that is not present in the second perovsite. Additionally or
alternatively, the second perovskite may for instance comprise a
doping agent that is not present in the first perovskite. Thus the
difference between the first and second perovskites may be the
presence or absence of a doping agent, or it may be the use of a
different doping agent in each perovskite. Alternatively, the first
and second perovskites may comprise the same doping agent. Thus the
difference between the first and second perovskites may not lie in
the doping agent but instead the difference may lie in the overall
structure of the first and second perovskites. In other words, the
first and second perovskites may be different perovskite
compounds.
[0162] Usually, in the optoelectronic device of the invention, the
perovskite of the charge transporting material is a perovskite
comprising a first cation, a second cation, and at least one
anion.
[0163] In some embodiments, the perovskite of the charge
transporting material is a perovskite compound of formula (IB):
[A][B][X].sub.3 (IB)
wherein: [A] is at least one organic cation or at least one group 1
metal cation; [B] is at least one metal cation; and [X] is said at
least one anion.
[0164] As the skilled person will appreciate, [A] may comprise
Cs.sup.+.
[0165] Usually, [B] comprises Pb.sup.2+ or Sn.sup.2+. More
typically, [B] comprises Pb.sup.2+.
[0166] Typically, [X] comprises a halide anion or a plurality of
different halide anions.
[0167] Usually, [X] comprises I.sup.-.
[0168] In some embodiments, [X] is two or more different anions,
for instance, two or more different halide anions. For instance,
[X] may comprise I.sup.- and F.sup.-, I.sup.- and Br.sup.- or
I.sup.- and Cl.sup.-.
[0169] Usually, in the optoelectronic device of the invention, the
perovskite compound of formula (IB) is CsPbI.sub.3 or CsSnI.sub.3.
For instance, the perovskite compound of formula (IB) may be
CsPbI.sub.3.
[0170] Alternatively, the perovskite compound of formula (IB) may
be CsPbI.sub.2Cl, CsPbICl.sub.2, CsPbI.sub.2F, CsPbIF.sub.2,
CsPbI.sub.2Br, CsPbTBr.sub.2, CsSnI.sub.2Cl, CsSnICl.sub.2,
CsSnI.sub.2F, CsSnIF.sub.2, CsSnI.sub.2Br or CsSnTBr.sub.2. For
instance, the perovskite compound of formula (IB) may be
CsPbI.sub.2Cl or CsPbICl.sub.2. Typically, the perovskite compound
of formula (IB) is CsPbICl.sub.2.
[0171] In the perovskite compound of formula (IB): [X] may be one,
two or more different anions as defined herein, for instance, one,
two or more different anions as defined herein for the first
perovskite; [A] usually comprises an organic cation as defined
herein, as above for the first perovskite; and [B] typically
comprises a metal cation as defined herein. The metal cation may be
defined as hereinbefore for the first perovskite.
[0172] In some embodiments, the perovskite of the charge
transporting material may be a perovskite as defined for the first
perovskite hereinabove. Again, the second perovskite may be the
same as or different from the first perovskite, typically it is
different.
[0173] Typically, in the optoelectronic device of the invention,
the charge transporting material is disposed within pores of said
porous dielectric scaffold material. Thus, when the optoelectronic
device of the invention comprises a layer comprising said porous
dielectric scaffold material and said semiconductor, the layer
usually further comprises said charge transporting material, within
pores of the porous dielectric scaffold material.
[0174] Typically, the optoelectronic device of the invention
comprises a photoactive layer, wherein the photoactive layer
comprises: said porous dielectric scaffold material; said
semiconductor; and said charge transporting material.
[0175] The term "photoactive layer", as used herein, refers to a
layer in the optoelectronic device which comprises a material that
(i) absorbs light, which may then generate free charge carriers; or
(ii) accepts charge, both electrons and holes, which may
subsequently recombine and emit light.
[0176] As would be understood by the skilled person when the
material absorbs light, the energy of the photon is used to promote
an electron to a higher energy state in the absorber. The photon
energy is converted into electrical potential energy.
[0177] Usually, in the photoactive layer, the semiconductor is an
n-type semiconductor as defined herein and the charge transporting
material is a hole transporting material as defined herein.
[0178] Alternatively, in the photoactive layer, the semiconductor
may be a p-type semiconductor as defined herein and the charge
transporting material may be an electron transporting material as
defined herein.
[0179] As a further alternatively, in the photoactive layer, the
semiconductor may be an intrinsic semiconductor as defined herein
and the charge transport material is a hole transport material as
defined herein or an electron transport material as defined
herein.
[0180] Typically, in the optoelectronic device of the invention, in
the photoactive layer, the semiconductor is a perovskite as defined
herein.
[0181] Usually, the photoactive layer comprises a layer comprising
said porous dielectric scaffold material and said semiconductor,
wherein the semiconductor is disposed on the surface of pores
within said dielectric scaffold material, and wherein said charge
transporting material is disposed within pores of said porous
dielectric scaffold material.
[0182] More typically, the photoactive layer comprises a layer
comprising said charge transporting material disposed on a layer
comprising said porous dielectric scaffold material and said
semiconductor, wherein the semiconductor is disposed on the surface
of pores within said dielectric scaffold material, and wherein the
device further comprises said charge transporting material disposed
within pores of said porous dielectric scaffold material.
[0183] Often, the thickness of the photoactive layer is from 100 nm
to 3000 nm. Usually, the thickness of the photoactive layer is from
100 nm to 1000 nm
[0184] As used herein, the term "thickness" refers to the average
thickness of a component of an optoelectronic device.
[0185] In one embodiment, the optoelectronic device of the
invention comprises:
[0186] a first electrode;
[0187] a second electrode; and disposed between the first and
second electrodes:
[0188] said photoactive layer.
[0189] The first and second electrodes are an anode and a cathode,
and usually one or both of the anode and cathode is transparent to
allow the ingress of light. The choice of the first and second
electrodes of the optoelectronic devices of the present invention
may depend on the structure type. Typically, the n-type layer is
deposited onto a tin oxide, more typically onto a fluorine-doped
tin oxide (FTO) anode, which is usually a transparent or
semi-transparent material. Thus, the first electrode is usually
transparent or semi-transparent and typically comprises FTO.
Usually, the thickness of the first electrode is from 200 nm to 600
nm, more usually, from 300 to 500 nm. For instance the thickness
may be 400 nm. Typically, FTO is coated onto a glass sheet.
Usually, the second electrode comprises a high work function metal,
for instance gold, silver, nickel, palladium or platinum, and
typically silver. Usually, the thickness of the second electrode is
from 50 nm to 250 nm, more usually from 100 nm to 200 nm. For
instance, the thickness of the second electrode may be 150 nm.
[0190] Typically, in the optoelectronic device of the invention,
the thickness of the photoactive layer is from 200 nm to 1000 nm,
for instance the thickness may be from 400 nm to 800 nm. Often,
thickness of the photoactive layer is from 400 nm to 600 nm.
Usually the thickness is about 500 nm.
[0191] Usually, the optoelectronic device of the invention
comprises:
[0192] a first electrode;
[0193] a second electrode; and disposed between the first and
second electrodes:
[0194] (a) said photoactive layer; and
[0195] (b) a compact layer comprising a metal oxide.
[0196] As the skilled person will appreciate, when the
semiconductor is an n-type semiconductor (for instance an n-type
perovskite, or a perovskite which acts as an n-type,
electron-transporting material when photo-doped) an n-type compact
layer should also be used. On the other hand, when the
semiconductor is p-type, the compact layer should be p-type too.
Examples of p-type semiconductors that can be used in the compact
layer include oxides of nickel, vanadium, copper or molybdenum.
Additionally, p-type organic hole-conductors may also be useful as
p-type compact layers. Examples of such p-type hole-conductors are
PEDO:PSS
(poly(3,4-ethylenedioxythiophene):poly-(styrenesulfonate)), and
polyanilene. Examples of n-type semiconductors that can be used in
the compact layer include oxides of titanium, tin, zinc, gallium,
niobium, tantalum, neodymium, palladium and cadmium, or a mixture
thereof, and sulphides of zinc or cadmium, or mixtures thereof.
[0197] Often, the semiconductor used in the compact layer will be
different from said semiconductor having a band gap of less than or
equal to 3.0 eV.
[0198] Alternatively, the semiconductor used in the compact layer
may be the same as said semiconductor having a band gap of less
than or equal to 3.0 eV. The compact layer may, for instance,
comprise said perovskite.
[0199] Often, the compact layer comprises a metal oxide or a metal
sulphide.
[0200] Usually, in the optoelectronic device of the invention, the
compact layer comprises an n-type semiconductor comprising an oxide
of titanium, tin, zinc, gallium, niobium, tantalum, neodymium,
palladium or cadmium, or a sulphide of zinc or cadmium.
[0201] Typically, in the optoelectronic device of the invention,
the compact layer comprises TiO.sub.2.
[0202] Usually, the compact layer has a thickness of from 20 nm to
200 nm, typically a thickness of about 100 nm.
[0203] Alternatively, in the optoelectronic device of the
invention, the compact layer may comprise a p-type semiconductor
comprising an oxide of nickel, vanadium or copper.
[0204] In one embodiment, in the optoelectronic device of the
invention, the compact layer may comprise a semiconductor
comprising an oxide of molybdenum or tungsten.
[0205] In one embodiment, the optoelectronic device of the
invention further comprises an additional layer, disposed between
the compact layer and the photoactive layer, which additional layer
comprises a metal oxide or a metal chalcogenide which is the same
as or different from the metal oxide or a metal chalcogenide
employed in the compact layer.
[0206] Typically, the additional layer comprises alumina, magnesium
oxide, cadmium sulphide, silicon dioxide, or yttrium oxide.
[0207] Usually, the optoelectronic device of the invention is
selected from a photovoltaic device; a photodiode; a
phototransistor; a photomultiplier; a photo resistor; a photo
detector; a light-sensitive detector; solid-state triode; a battery
electrode; a light-emitting device; a light-emitting diode; a
transistor; a solar cell; a laser; and a diode injection laser.
[0208] In a preferred embodiment, the optoelectronic device of the
invention is a photovoltaic device.
[0209] Usually, the optoelectronic device of the invention is a
solar cell.
[0210] In an alternative embodiment, the optoelectronic device of
the invention is a light-emitting device, for instance a
light-emitting diode.
[0211] In one embodiment the optoelectronic device of the invention
is a photovoltaic device, wherein the device comprises:
[0212] a first electrode;
[0213] a second electrode; and disposed between the first and
second electrodes:
[0214] a photoactive layer;
[0215] wherein the photoactive layer comprises a charge
transporting material and a layer comprising (i) said porous
dielectric scaffold material and (ii) said semiconductor, wherein
the semiconductor is a photosensitizing material and is disposed on
the surface of pores within said dielectric scaffold material, and
wherein said charge transporting material is disposed within pores
of said porous dielectric scaffold material; and said semiconductor
comprises a perovskite which is a perovskite compound of formula
(I):
[A][B][X].sub.3 (I)
wherein:
[0216] [A] is at least one organic cation;
[0217] [B] is at least one metal cation; and
[0218] [X] is at least one anion selected from halide anions and
chalcogenide anions.
[0219] The organic and metal cations may be as further defined
hereinbefore. Thus the organic cations may be selected from cations
of formula (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+ and cations of
formula (R.sub.5NH.sub.3).sup.+, as defined above. The metal
cations may be selected from divalent metal cations. For instance,
the metal cations may be selected from Ca.sup.2+, Sr.sup.2+,
Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+,
Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+
and Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or
Pb.sup.2+.
[0220] The organic cations may, for instance, be selected from
cations of formula (R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+
and cations of formula (H.sub.2N.dbd.CH--NH.sub.2).sup.+, as
defined above. The metal cations may be selected from divalent
metal cations. For instance, the metal cations may be selected from
Ca.sup.2+, Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+,
Fe.sup.2+, Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+,
Sn.sup.2+, Yb.sup.2+ and Eu.sup.2+. Usually, the metal cation is
Sn.sup.2+ or Pb.sup.2+.
[0221] [X] may also be as further defined herein. Usually, [X] is
two or more different anions selected from halide anions and
chalcogenide anions. More typically, [X] is two or more different
halide anions.
[0222] The porous dielectric scaffold material and the charge
transporting material may also be as further defined herein.
[0223] In a further embodiment the optoelectronic device of the
invention is a photovoltaic device, wherein the device
comprises:
[0224] a first electrode;
[0225] a second electrode; and disposed between the first and
second electrodes:
[0226] a compact layer comprising a metal oxide; and
[0227] a photoactive layer;
[0228] wherein the photoactive layer comprises a charge
transporting material and a layer comprising said porous dielectric
scaffold material and said semiconductor, wherein the semiconductor
is a photosensitizing material and is disposed on the surface of
pores within said dielectric scaffold material, and wherein said
charge transporting material is disposed within pores of said
porous dielectric scaffold material; and
[0229] said semiconductor comprises a perovskite which is a
perovskite compound of formula (I):
[A][B][X].sub.3 (I)
wherein:
[0230] [A] is at least one organic cation;
[0231] [B] is at least one metal cation; and
[0232] [X] is at least one anion selected from halide anions and
chalcogenide anions.
[0233] The organic and metal cations may be as further defined
hereinbefore. Thus the organic cations may be selected from cations
of formula (R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+ and cations of
formula (R.sub.5NH.sub.3).sup.+, as defined above. The metal
cations may be selected from divalent metal cations. For instance,
the metal cations may be selected from Ca.sup.2+, Sr.sup.2+,
Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+,
Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+, Yb.sup.2+
and Eu.sup.2+. Usually, the metal cation is Sn.sup.2+ or
Pb.sup.2+.
[0234] The organic cations may, for instance, be selected from
cations of formula (R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+
and cations of formula (H.sub.2N.dbd.CH--NH.sub.2).sup.+, as
defined above. The metal cations may be selected from divalent
metal cations. For instance, the metal cations may be selected from
Ca.sup.2+, Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+,
Fe.sup.2+, Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+,
Sn.sup.2+, Yb.sup.2+ and Eu.sup.2+. Usually, the metal cation is
Sn.sup.2+ or Pb.sup.2+.
[0235] [X] may also be as further defined herein. Usually, [X] is
two or more different anions selected from halide anions and
chalcogenide anions. More typically, [X] is two or more different
halide anions.
[0236] The porous dielectric scaffold material and the hole
transporting material may also be as further defined herein, as may
be the metal oxide in the compact layer.
[0237] Usually, the semiconductor is an n-type semiconductor and
the charge transporting material is a hole transporting material as
defined herein.
[0238] Alternatively, the semiconductor is a p-type semiconductor
and the charge transporting material is an electron transporting
material as defined herein.
[0239] The fundamental losses in a solar cell can be quantified as
the difference in energy between the open-circuit voltage and the
band-gap of the absorber, which may be considered the loss in
potential. The theoretical maximum open-circuit voltage can be
estimated as a function of band gap following the Schokley-Quasar
treatment, and for a material with a band gap of 1.55 eV the
maximum possible open-circuit voltage under full sun illumination
is 1.3 V, giving a minimum loss-in-potential 0.25 eV.
[0240] Often, in the optoelectronic device of the invention, x is
less than or equal to 0.6 eV, wherein:
x is equal to A-B,
wherein:
[0241] A is the optical band gap of said thin-film semiconductor;
and
[0242] B is the open-circuit voltage generated by the
optoelectronic device under standard AM1.5G 100 mWcm.sup.-2 solar
illumination.
[0243] Usually, in the optoelectronic device of the invention, x is
less than or equal to 0.45 eV.
[0244] The invention also provides the use of: (i) a porous
dielectric scaffold material; and (ii) a semiconductor having a
band gap of less than or equal to 3.0 eV, in contact with the
scaffold material; in an optoelectronic device.
[0245] Often, in the use of the invention, the use is of: (i) a
porous dielectric scaffold material; and (ii) a semiconductor
having a band gap of less than or equal to 3.0 eV, which is in
contact with the scaffold material, as a photoactive material in an
optoelectronic device.
[0246] Typically, the use is of: (i) said porous dielectric
scaffold material; (ii) said semiconductor, in contact with the
scaffold material; and (iii) a charge transporting material; as a
photoactive material in an optoelectronic device.
[0247] The invention also provides the use of a layer comprising:
(i) a porous dielectric scaffold material; and (ii) a semiconductor
having a band gap of less than or equal to 3.0 eV, in contact with
the scaffold material; as a photoactive layer in an optoelectronic
device.
[0248] Typically, the layer further comprises a charge transporting
material.
[0249] In the uses of the invention the porous dielectric scaffold
material may be as further defined herein; and/or the semiconductor
may be as further defined herein. The charge transporting material
may also be as further defined herein.
[0250] Usually, the semiconductor comprises an n-type semiconductor
comprising a perovskite.
[0251] Alternatively, in one embodiment, in the uses of the
invention, the semiconductor is a p-type semiconductor.
[0252] Typically, the semiconductor comprises a p-type
semiconductor comprising a perovskite.
[0253] In some embodiments, the semiconductor comprises an oxide of
gallium, niobium, tantalum, tungsten, indium, neodymium or
palladium, or a sulphide of zinc or cadmium, provided of course
that the semiconductor has a band gap of less than or equal to 3.0
eV.
[0254] Additionally or alternatively, in some embodiments, the
semiconductor comprises an oxide of nickel, vanadium, lead, copper
or molybdenum, provided of course that the semiconductor has a band
gap of less than or equal to 3.0 eV.
[0255] In another embodiment, in the uses of the invention, the
semiconductor is an intrinsic semiconductor.
[0256] Often, the semiconductor comprises an intrinsic
semiconductor comprises a perovskite.
[0257] Typically, in the uses of the invention, the semiconductor
is disposed on the surface of said porous dielectric scaffold
material. Thus, usually, the semiconductor is disposed on the
surfaces of pores within said porous dielectric scaffold
material.
[0258] Also, the charge transporting material, where present, is
typically disposed within pores of said porous dielectric scaffold
material. Often, the charge transporting material is a hole
transporting material as defined herein. Alternatively, the charge
transporting material is an electron transporting material as
defined herein.
[0259] In one embodiment, in the uses of the invention, (a) the
porous dielectric scaffold material comprises an oxide of
aluminium, germanium, zirconium, silicon, yttrium or ytterbium; or
alumina silicate; and/or (b) the semiconductor is a perovskite.
[0260] For instance, in the uses of the invention, (a) the porous
dielectric scaffold material is as further defined herein; and/or
(b) the semiconductor is as further defined herein.
[0261] Typically, in the uses of the invention, the optoelectronic
device is a photovoltaic device. Usually, the optoelectronic device
is a solar cell.
[0262] Alternatively, in the uses of the invention, the
optoelectronic device may be a light-emitting device, for instance
a light-emitting diode.
[0263] The invention also provides a photoactive layer for an
optoelectronic device comprising: (a) a porous dielectric scaffold
material; (b) a semiconductor having a band gap of less than or
equal to 3.0 eV, in contact with the scaffold material; and (c) a
charge transporting material.
[0264] Typically, in the photoactive layer of the invention, the
semiconductor is disposed on the surface of said porous dielectric
scaffold material. Thus, usually, the semiconductor is disposed on
the surfaces of pores within said porous dielectric scaffold
material. Also, the charge transporting material is typically
disposed within pores of said porous dielectric scaffold
material.
[0265] Usually, in the photoactive layer of the invention, the
semiconductor is an n-type semiconductor. Typically, the
semiconductor comprises an n-type semiconductor comprising a
perovskite,
[0266] Alternatively, in the photoactive layer of the invention,
the semiconductor may be a p-type semiconductor. Often, the
semiconductor comprises a p-type semiconductor comprising a
perovskite,
[0267] As a further alternative, in the photoactive layer of the
invention, the semiconductor may be an intrinsic semiconductor.
Usually, the semiconductor comprises an intrinsic semiconductor
comprises a perovskite
[0268] In some embodiments, in the photoactive layer, the
semiconductor comprises an oxide of gallium, niobium, tantalum,
tungsten, indium, neodymium or palladium, or a sulphide of zinc or
cadmium, provided of course that the semiconductor has a band gap
of less than or equal to 3.0 eV.
[0269] Additionally or alternatively, in some embodiments, in the
photoactive layer, the semiconductor comprises an oxide of nickel,
vanadium, lead, copper or molybdenum, provided of course that the
semiconductor has a band gap of less than or equal to 3.0 eV.
[0270] Typically, in the photoactive layer of the invention: (a)
the porous dielectric scaffold material comprises an oxide of
aluminium, germanium, zirconium, silicon, yttrium or ytterbium; or
alumina silicate; (b) the semiconductor is a perovskite; and/or (c)
the charge transporting material is a hole transporting
material.
[0271] For instance, (a) the porous dielectric scaffold material
may be as further defined herein; (b) the semiconductor may be as
further defined herein; and/or (c) the charge transporting material
may be as further defined herein.
[0272] Alternatively, often, in the photoactive layer of the
invention: (a) the porous dielectric scaffold material comprises an
oxide of aluminium, germanium, zirconium, silicon, yttrium or
ytterbium; or alumina silicate; (b) the semiconductor is a
perovskite; and/or (c) the charge transporting material is an
electron conductor.
[0273] For instance, (a) the porous dielectric scaffold material
may be as further defined herein; (b) the semiconductor is as
further defined herein; and/or (c) the charge transporting material
is as further defined herein.
[0274] The porous dielectric scaffold material used in the devices
of the invention can be produced by a process comprising: (i)
washing a first dispersion of a dielectric material; and (ii)
mixing the washed dispersion with a solution comprising a
pore-forming agent which is a combustible or dissolvable organic
compound. The pore-forming agent is removed later in the process by
burning the agent off or by selectively dissolving it using an
appropriate solvent. Any suitable pore-forming agent may be used.
The pore-forming agent may be a carbohydrate, for instance a
polysaccharide, or a derivative thereof. Typically, ethyl cellulose
is used as the pore-forming agent.
[0275] The term "carbohydrate" refers to an organic compound
consisting of carbon, oxygen and hydrogen. The hydrogen to oxygen
atom ratio is usually 2:1. It is to be understood that the term
carbohydrate encompasses monosaccharides, disaccharides,
oligosaccharides and polysaccharides. Carbohydrate derivatives are
typically carbohydrates comprising additional substituents. Usually
the substituents are other than hydroxyl groups. When an
carbohydrate is substituted it typically bears one or more
substituents selected from substituted or unsubstituted
C.sub.1-C.sub.20 alkyl, substituted or unsubstituted aryl, cyano,
amino, C.sub.1-C.sub.10 alkylamino, di(C.sub.1-C.sub.10)alkylamino,
arylamino, diarylamino, arylalkylamino, amido, acylamido, oxo,
halo, carboxy, ester, acyl, acyloxy, C.sub.1-C.sub.20 alkoxy,
aryloxy, haloalkyl, sulfonic acid, sulfhydryl (i.e. thiol, --SH),
C.sub.1-C.sub.10 alkylthio, arylthio, sulfonyl, phosphoric acid,
phosphate ester, phosphonic acid and phosphonate ester. Examples of
substituted alkyl groups include haloalkyl, hydroxyalkyl,
aminoalkyl, alkoxyalkyl and alkaryl groups. The term alkaryl, as
used herein, pertains to a C.sub.1-C.sub.20 alkyl group in which at
least one hydrogen atom has been replaced with an aryl group.
Examples of such groups include, but are not limited to, benzyl
(phenylmethyl, PhCH.sub.2--), benzhydryl (Ph.sub.2CH--), trityl
(triphenylmethyl, Ph.sub.3C--), phenethyl (phenylethyl,
Ph-CH.sub.2CH.sub.2--), styryl (Ph-CH.dbd.CH--), cinnamyl
(Ph-CH.dbd.CH--CH.sub.2--). In a carbohydrate derivative, the
substituent on the carbohydrate may, for instance, be a
C.sub.1-C.sub.6 alkyl, wherein a C.sub.1-C.sub.6 alkyl is as
defined herein above. Often the substituents are substituents on
the hydroxyl group of the carbohydrate. Typically, the pore-forming
agent used in the step of mixing the dispersion with a solution is
a carbohydrate or a derivative thereof, more typically a
carbohydrate derivative. Thus, for instance, the carbohydrate or a
derivative thereof is ethyl cellulose.
[0276] Usually, the first dispersion used in the process for
producing the porous dielectric scaffold material is a solution
comprising an electrolyte and water. Typically, the first
dispersion is about 10 wt % of the electrolyte in water. For some
dielectrics, for instance, silica, the process further comprises a
step of forming the electrolyte from a precursor material. For
instance, when the dielectric is silica, the process may further
comprises a step of forming the electrolyte from a silicate, such
as tetraethyl orthosilicate. Usually the precursor material is
added to water. Typically, the first dispersion is produced by
mixing an alcohol, such as ethanol, with water, then adding a base,
such as ammonium hydroxide, in water and the precursor material.
When the dielectric is silica, usually from 2 to 3 ml of deionized
water are added to from 55 to 65 ml of absolute ethanol. Typically,
about 2.52 ml of deionized water are added to about 59.2 ml of
absolute ethanol.
[0277] This mixture is usually then stirred vigorously. Then,
typically, from 0.4 to 0.6 ml of the base in water are added along
with from 5 to 10 ml of the precursor. More typically, about 0.47
ml of ammonium hydroxide 28% in water are added along with about
7.81 ml of the precursor.
[0278] In the step of washing the first dispersion of a dielectric
material often the first dispersion is centrifuged at from 6500 to
8500 rpm, usually at about 7500 rpm. Usually, the first dispersion
is centrifuged for from 2 to 10 hours, typically for about 6 hours.
The centrifuged dispersion is then usually redispersed in an
alcohol, such as absolute ethanol. Often, the centrifuged
dispersion is redispersed in an alcohol with an ultrasonic probe.
The ultrasonic probe is usually operated for a total sonication
time of from 3 minutes to 7 minutes, often about 5 minutes.
Typically, the sonication is carried out in cycles. Usually,
sonication is carried out in cycles of approximately 2 seconds on
and approximately 2 seconds off. The step of washing the first
dispersion is often repeated two, three or four times, typically
three times.
[0279] Usually, in the step of mixing the washed dispersion with a
solution comprising a carbohydrate or a derivative thereof, the
solution comprises a solvent for the carbohydrate or a derivative
thereof. For instance, when the carbohydrate or a derivative
thereof is ethyl cellulose, the solvent may be
.alpha.-terpineol.
[0280] Typically, the amount of the product from the step of
washing the first dispersion used in the step of mixing the washed
dispersion with the solution is equivalent to using from 0.5 to 1.5
g of the dielectric, for instance, about 1 g of the dielectric.
When the carbohydrate or derivative thereof is ethyl cellulose,
usually, a mix of different grades of ethyl cellulose are used.
Typically a ratio of approximately 50:50 of 10 cP:46 cP of ethyl
cellulose is used. Usually, from 4 to 6 g of the carbohydrate or
derivative is used. More usually, about 5 g of the carbohydrate or
derivative is used. Typically the amount of solvent used is from 3
to 3.5 g, for instance 3.33 g.
[0281] Typically, in the step of mixing the washed dispersion with
a solution comprising a carbohydrate or a derivative thereof, each
component is added in turn. Usually, after each component is added,
the mixture is stirred for from 1 to 3 minutes, for instance, for 2
minutes. Often, after the mixture is stirred, it is sonicated with
an ultrasonic probe for a total sonication time of from 30 to 90
seconds, often about 1 minute. Typically, the sonication is carried
out in cycles. Usually, sonication is carried out in cycles of
approximately 2 seconds on and approximately 2 seconds off.
[0282] Usually, in the step of mixing the washed dispersion with a
solution comprising a carbohydrate or a derivative thereof, after
the components have been mixed, the resulting mixture is introduced
into a rotary evaporator. The rotary evaporator is typically used
to remove any excess alcohol, such as ethanol, and/or to achieve a
thickness of solution appropriate for spin coating, doctor blading
or screen printing the material.
[0283] The perovskite used in the devices of the invention, can be
produced by a process comprising mixing:
[0284] (a) a first compound comprising (i) a first cation and (ii)
a first anion; with
[0285] (b) a second compound comprising (i) a second cation and
(ii) a second anion:
[0286] wherein:
[0287] the first and second cations are as defined herein; and
[0288] the first and second anions may be the same or different
anions.
[0289] The perovskites which comprise at least one anion selected
from halide anions and chalcogenide anions, may, for instance, be
produced by a process comprising mixing:
[0290] (a) a first compound comprising (i) a first cation and (ii)
a first anion; with
[0291] (b) a second compound comprising (i) a second cation and
(ii) a second anion:
[0292] wherein:
[0293] the first and second cations are as herein defined; and
[0294] the first and second anions may be the same or different
anions selected from halide anions and chalcogenide anions.
Typically, the first and second anions are different anions. More
typically, the first and second anions are different anions
selected from halide anions.
[0295] The perovskite produced by the process may comprise further
cations or further anions. For example, the perovskite may comprise
two, three or four different cations, or two, three of four
different anions. The process for producing the perovskite may
therefore comprise mixing further compounds comprising a further
cation or a further anion. Additionally or alternatively, the
process for producing the perovskite may comprise mixing (a) and
(b) with: (c) a third compound comprising (i) the first cation and
(ii) the second anion; or (d) a fourth compound comprising (i) the
second cation and (ii) the first anion.
[0296] Typically, in the process for producing the perovskite, the
second cation in the mixed-anion perovskite is a metal cation. More
typically, the second cation is a divalent metal cation. For
instance, the first cation may be selected from Ca.sup.2+,
Sr.sup.2+, Cd.sup.2+, Cu.sup.2+, Ni.sup.2+, Mn.sup.2+, Fe.sup.2+,
Co.sup.2+, Pd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Sn.sup.2+,
Y.sup.2+ and Eu.sup.2+. Usually, the second cation is selected from
Sn.sup.2+ and Pb.sup.2+.
[0297] Often, in the process for producing the perovskite, the
first cation in the mixed-anion perovskite is an organic
cation.
[0298] Usually, the organic cation has the formula
(R.sub.1R.sub.2R.sub.3R.sub.4N).sup.+, wherein:
[0299] R.sub.1 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
[0300] R.sub.2 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
[0301] R.sub.3 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl;
and
[0302] R.sub.4 is hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, or unsubstituted or substituted aryl.
[0303] Mainly, in the organic cation, R.sub.1 is hydrogen, methyl
or ethyl, R.sub.2 is hydrogen, methyl or ethyl, R.sub.3 is
hydrogen, methyl or ethyl, and R.sub.4 is hydrogen, methyl or
ethyl. For instance R.sub.1 may be hydrogen or methyl, R.sub.2 may
be hydrogen or methyl, R.sub.3 may be hydrogen or methyl, and
R.sub.4 may be hydrogen or methyl.
[0304] Alternatively, the organic cation may have the formula
(R.sub.5NH.sub.3).sup.+, wherein: R.sub.5 is hydrogen, or
unsubstituted or substituted C.sub.1-C.sub.20 alkyl. For instance,
R.sub.5 may be methyl or ethyl. Typically, R.sub.5 is methyl.
[0305] In some embodiments, the organic cation has the formula
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, wherein: R.sub.5
is hydrogen, unsubstituted or substituted C.sub.1-C.sub.20 alkyl,
or unsubstituted or substituted aryl; R.sub.6 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; R.sub.7 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; and R.sub.8 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl. The organic cation may, for
instance, be (R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+,
wherein: R.sub.5, R.sub.6, R.sub.7 and R.sub.8 are independently
selected from hydrogen, unsubstituted or substituted
C.sub.1-C.sub.20 alkyl, and unsubstituted or substituted aryl. For
instance, the organic cation may be
(H.sub.2N.dbd.CH--NH.sub.2).sup.+.
[0306] In the process for producing the perovskite, the perovskite
is usually a mixed-halide perovskite, wherein said two or more
different anions are two or more different halide anions.
[0307] Typically, in the process for producing the perovskite, the
perovskite is a perovskite compound of the formula (I):
[A][B][X].sub.3 (I)
wherein:
[0308] [A] is at least one organic cation;
[0309] [B] is at least one metal cation; and
[0310] [X] is said two or more different anions; and
the process comprises mixing:
[0311] (a) a first compound comprising (i) a metal cation and (ii)
a first anion; with
[0312] (b) a second compound comprising (i) an organic cation and
(ii) a second anion:
[0313] wherein:
[0314] the first and second anions are different anions selected
from halide anions or chalcogenide anions.
[0315] Alternatively the process may comprising (1) treating: (a) a
first compound comprising (i) a first cation and (ii) a first
anion; with (b) a second compound comprising (i) a second cation
and (ii) a first anion, to produce a first product, wherein: the
first and second cations are as herein defined; and the first anion
is selected from halide anions and chalcogenide anions; and (2)
treating (a) a first compound comprising (i) a first cation and
(ii) a second anion; with (b) a second compound comprising (i) a
second cation and (ii) a second anion, to produce a second product,
wherein: the first and second cations are as herein defined; and
the second anion is selected from halide anions and chalcogenide
anions. Usually, the first and second anions are different anions
selected from halide anions and chalcogenide anions. Typically, the
first and second anions are different anions selected from halide
anions. The process usually further comprises treating a first
amount of the first product with a second amount of the second
product, wherein the first and second amounts may be the same or
different.
[0316] The perovskite of the formula (I) may, for instance,
comprise one, two, three or four different metal cations, typically
one or two different metal cations. The perovskite of the formula
(I), may, for instance, comprise one, two, three or four different
organic cations, typically one or two different organic cations.
The perovskite of the formula (I), may, for instance, comprise two,
three or four different anions, typically two or three different
anions. The process may, therefore, comprising mixing further
compounds comprising a cation and an anion.
[0317] Typically, [X] is two or more different halide anions. The
first and second anions are thus typically halide anions.
Alternatively [X] may be three different halide ions. Thus the
process may comprise mixing a third compound with the first and
second compound, wherein the third compound comprises (i) a cation
and (ii) a third halide anion, where the third anion is a different
halide anion from the first and second halide anions.
[0318] Often, in the process for producing the perovskite, the
perovskite is a perovskite compound of the formula (IA):
AB[X].sub.3 (IA)
wherein:
[0319] A is an organic cation;
[0320] B is a metal cation; and
[0321] [X] is said two or more different anions.
the process comprises mixing:
[0322] (a) a first compound comprising (i) a metal cation and (ii)
a first halide anion; with
[0323] (b) a second compound comprising (i) an organic cation and
(ii) a second halide anion:
wherein:
[0324] the first and second halide anions are different halide
anions.
[0325] Usually, [X] is two or more different halide anions.
Preferably, [X] is two or three different halide anions. More
preferably, [X] is two different halide anions. In another
embodiment [X] is three different halide anions.
[0326] Typically, in the process for producing the perovskite, the
perovskite is a perovskite compound of formula (II):
ABX.sub.3-yX'.sub.y (II)
wherein:
[0327] A is an organic cation;
[0328] B is a metal cation;
[0329] X is a first halide anion;
[0330] X' is a second halide anion which is different from the
first halide anion; and
[0331] y is from 0.05 to 2.95; and
the process comprises mixing:
[0332] (a) a first compound comprising (i) a metal cation and (ii)
X; with
[0333] (b) a second compound comprising (i) an organic cation and
(ii) X':
wherein the ratio of X to X' in the mixture is equal to
(3-y):y.
[0334] In order to achieve said ratio of X to X' equal to (3-y):y,
the process may comprise mixing a further compound with the first
and second compounds. For example, the process may comprise mixing
a third compound with the first and second compounds, wherein the
third compound comprises (i) the metal cation and (ii) X'.
Alternative, the process may comprising mixing a third compound
with the first and second compounds, wherein the third compound
comprises (i) the organic cation and (ii) X.
[0335] Usually, y is from 0.5 to 2.5, for instance from 0.75 to
2.25. Typically, y is from 1 to 2.
[0336] Typically, in the process for producing the perovskite, the
first compound is BX.sub.2 and the second compound is AX'.
[0337] Often the second compound is produce by reacting a compound
of the formula (R.sub.5NH.sub.2), wherein: R.sub.5 is hydrogen, or
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, with a
compound of formula HX'. Typically, R.sub.5 may be methyl or ethyl,
often R.sub.5 is methyl.
[0338] Usually, the compound of formula (R.sub.5NH.sub.2) and the
compound of formula HX' are reacted in a 1:1 molar ratio. Often,
the reaction takes place under nitrogen atmosphere and usually in
anhydrous ethanol. Typically, the anhydrous ethanol is about 200
proof. More typically from 15 to 30 ml of the compound of formula
(R.sub.5NH.sub.2) is reacted with about 15 to 15 ml of HX', usually
under nitrogen atmosphere in from 50 to 150 ml anhydrous ethanol.
The process may also comprise a step of recovering said mixed-anion
perovskite. A rotary evaporator is often used to extract
crystalline AX'.
[0339] Usually, the step of mixing the first and second compounds
is a step of dissolving the first and second compounds in a
solvent. The first and second compounds may be dissolved in a ratio
of from 1:20 to 20:1, typically a ratio of 1:1. Typically the
solvent is dimethylformamide (DMF) or water. When the metal cation
is Pb.sup.2+ the solvent is usually dimethylformamide. When the
metal cation is Sn.sup.2+ the solvent is usually water. The use of
DMF or water as the solvent is advantageous as these solvents are
not very volatile.
[0340] Often, in the process for producing the perovskite, the
perovskite is a perovskite selected from CH.sub.3NH.sub.3PbI.sub.3,
CH.sub.3NH.sub.3PbBr.sub.3, CH.sub.3NH.sub.3PbCl.sub.3,
CH.sub.3NH.sub.3PbF.sub.3, CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3SnBrI.sub.2,
CH.sub.3NH.sub.3SnBrCl.sub.2, CH.sub.3NH.sub.3SnF.sub.2Br,
CH.sub.3NH.sub.3SnIBr.sub.2, CH.sub.3NH.sub.3SnICl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2I, CH.sub.3NH.sub.3SnClBr.sub.2,
CH.sub.3NH.sub.3SnI.sub.2Cl and CH.sub.3NH.sub.3SnF.sub.2Cl. More
often, the perovskite is a perovskite selected from
CH.sub.3NH.sub.3PbBrI.sub.2, CH.sub.3NH.sub.3PbBrCl.sub.2,
CH.sub.3NH.sub.3PbIBr.sub.2, CH.sub.3NH.sub.3PbICl.sub.2,
CH.sub.3NH.sub.3PbClBr.sub.2, CH.sub.3NH.sub.3PbI.sub.2Cl,
CH.sub.3NH.sub.3SnBrI.sub.2, CH.sub.3NH.sub.3SnBrCl.sub.2,
CH.sub.3NH.sub.3SnF.sub.2Br, CH.sub.3NH.sub.3 SnIBr.sub.2,
CH.sub.3NH.sub.3SnICl.sub.2, CH.sub.3NH.sub.3SnF.sub.2I,
CH.sub.3NH.sub.3 SnClBr.sub.2, CH.sub.3NH.sub.3SnI.sub.2Cl and
CH.sub.3NH.sub.3SnF.sub.2Cl. Typically, the perovskite is selected
from CH.sub.3NH.sub.3PbBrI.sub.2, CH.sub.3NH.sub.3PbBrCl.sub.2,
CH.sub.3NH.sub.3PbIBr.sub.2, CH.sub.3NH.sub.3PbICl.sub.2,
CH.sub.3NH.sub.3PbClBr.sub.2, CH.sub.3NH.sub.3PbI.sub.2Cl,
CH.sub.3NH.sub.3 SnF.sub.2Br, CH.sub.3NH.sub.3SnICl.sub.2,
CH.sub.3NH.sub.3 SnF.sub.2I, CH.sub.3NH.sub.3SnI.sub.2Cl and
CH.sub.3NH.sub.3SnF.sub.2Cl. More typically, the perovskite is
selected from CH.sub.3NH.sub.3PbBrI.sub.2,
CH.sub.3NH.sub.3PbBrCl.sub.2, CH.sub.3NH.sub.3PbIBr.sub.2,
CH.sub.3NH.sub.3PbICl.sub.2, CH.sub.3NH.sub.3PbClBr.sub.2,
CH.sub.3NH.sub.3PbI.sub.2Cl, CH.sub.3NH.sub.3SnF.sub.2Br,
CH.sub.3NH.sub.3SnF.sub.2I and CH.sub.3NH.sub.3SnF.sub.2Cl.
Usually, the perovskite is selected from
CH.sub.3NH.sub.3PbBrI.sub.2, CH.sub.3NH.sub.3PbBrCl.sub.2,
CH.sub.3NH.sub.3PbIBr.sub.2, CH.sub.3NH.sub.3PbICl.sub.2,
CH.sub.3NH.sub.3 SnF.sub.2Br, and CH.sub.3NH.sub.3SnF.sub.2I.
[0341] In some embodiments, in the process for producing the
mixed-anion perovskite, the perovskite is a perovskite compound of
formula (IIa):
ABX.sub.3zX'.sub.3(1-z) (IIa)
wherein:
[0342] A is an organic cation of the formula
(R.sub.5R.sub.6N.dbd.CH--NR.sub.7R.sub.8).sup.+, wherein: (i)
R.sub.5 is hydrogen, unsubstituted or substituted C.sub.1-C.sub.20
alkyl, or unsubstituted or substituted aryl; (ii) R.sub.6 is
hydrogen, unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; (iii) R.sub.7 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl; and (iv) R.sub.8 is hydrogen,
unsubstituted or substituted C.sub.1-C.sub.20 alkyl, or
unsubstituted or substituted aryl;
[0343] B is an metal cation selected from Sn.sup.2+ and
Pb.sup.2+;
[0344] X is a first halide anion;
[0345] X' is a second halide anion which is different from the
first halide anion; and
[0346] z is greater than 0 and less than 1;
and the process comprises (1) treating: (a) a first compound
comprising (i) the metal cation and (ii) X, with (b) a second
compound comprising (i) the organic cation and (ii) X, to produce a
first product; (2) treating: (a) a first compound comprising (i)
the metal cation and (ii) X', with (b) a second compound comprising
(i) the organic cation and (ii) X', to produce a second product;
and (3) treating a first amount of the first product with a second
amount of the second product, wherein the first and second amounts
may be the same or different.
[0347] Usually z is from 0.05 to 0.95.
[0348] In the process for producing a mixed-anion perovskite, the
perovskite may, for instance, have the formula
(H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3zBr.sub.3(1-z), wherein z is as
defined hereinabove.
[0349] Other semiconductors used in the devices of the invention
may be prepared using known synthetic techniques.
[0350] The photoactive layer of the invention, or the photoactive
layer present in the optoelectronic device of the invention, may
further comprise encapsulated metal nanoparticles.
[0351] The process for producing an optoelectronic device is
usually a process for producing a device selected from: a
photovoltaic device; a photodiode; a phototransistor; a
photomultiplier; a photo resistor; a photo detector; a
light-sensitive detector; solid-state triode; a battery electrode;
a light-emitting device; a light-emitting diode; a transistor; a
solar cell; a laser; and a diode injection laser. Typically, the
optoelectronic device is a photovoltaic device. Alternatively, the
optoelectronic device may be a light-emitting device.
[0352] The process for producing an optoelectronic device of the
invention, wherein the optoelectronic device comprises:
[0353] a first electrode;
[0354] a second electrode; and disposed between the first and
second electrodes:
[0355] a photoactive layer, which photoactive layer comprises a
porous dielectric scaffold material and a semiconductor having a
band gap of less than or equal to 3.0 eV, in contact with the
scaffold material;
is usually a process comprising:
[0356] (i) providing a first electrode;
[0357] (ii) depositing said photoactive layer; and
[0358] (iii) providing a second electrode.
[0359] As the skilled person will appreciate, the process of
producing an optoelectronic device will vary depending on the
optoelectronic device being made, and in particular depending upon
the different components of the device. The process which is
discussed below and exemplified is a process for producing an
optoelectronic device which comprises a first electrode; a second
electrode; and disposed between the first and second electrodes:
(a) a photoactive layer comprising: (i) a charge transporting
material, which is a hole transporting material; (ii) a layer
comprising said porous dielectric scaffold material and (iii) a
semiconductor, which semiconductor is a perovskite, wherein the
semiconductor is a photosensitizing material and is disposed on the
surface of pores within said dielectric scaffold material, and
wherein said charge transporting material is disposed within pores
of said porous dielectric scaffold material; and (b) a compact
layer comprising an n-type semiconductor. However, as the skilled
person will appreciate, the same process may be used or adapted to
produce other devices of the invention, having different components
and different layer structures. These include, for instance,
optoelectronic devices of the invention which comprise: a first
electrode; a second electrode; and disposed between the first and
second electrodes: (a) a photoactive layer comprising: (i) a charge
transporting material, which is an electron transporting material;
(ii) a layer comprising said porous dielectric scaffold material
and (iii) a semiconductor, which semiconductor is a perovskite; and
(b) a compact layer comprising an-type semiconductor. Also, the
process described herein can be used to produce optoelectronic
devices comprising: a first electrode; a second electrode; and
disposed between the first and second electrodes: a photoactive
layer comprising: (i) a layer comprising said porous dielectric
scaffold material and (ii) a semiconductor having a band gap of
less than or equal to 3.0 eV, which semiconductor is any suitable
n-type semiconductor, any suitable p-type semiconductor or any
suitable intrinsic semiconductor, or, for instance, optoelectronic
devices comprising a first electrode; a second electrode; and
disposed between the first and second electrodes: (a) a photoactive
layer comprising: (i) a charge transporting material, which is an
hole transporting material; (ii) a layer comprising said porous
dielectric scaffold material and (iii) a semiconductor having a
band gap of less than or equal to 3.0 eV, which semiconductor is
any suitable n-type semiconductor; and (b) a compact layer
comprising an n-type semiconductor, or, for instance,
optoelectronic devices comprising a first electrode; a second
electrode; and disposed between the first and second electrodes:
(a) a photoactive layer comprising: (i) a charge transporting
material, which is an electron transporting material; (ii) a layer
comprising said porous dielectric scaffold material and (iii) a
semiconductor having a band gap of less than or equal to 3.0 eV,
which semiconductor is any suitable p-type semiconductor; and (b) a
compact layer comprising a p-type semiconductor.
[0360] The process for producing an optoelectronic device of the
invention, wherein the optoelectronic device comprises:
[0361] a first electrode;
[0362] a second electrode; and disposed between the first and
second electrodes:
[0363] (a) said photoactive layer; and
[0364] (b) a compact layer comprising a metal oxide.
is usually a process comprising:
[0365] (i) providing a first electrode;
[0366] (ii) depositing said photoactive layer;
[0367] (iii) depositing said compact layer; and
[0368] (iv) providing a second electrode.
[0369] The first and second electrodes are an anode and a cathode,
one or both of which is transparent to allow the ingress of light.
The choice of the first and second electrodes of the optoelectronic
devices of the present invention may depend on the structure type.
Typically, the n-type layer is deposited onto a tin oxide, more
typically onto a fluorine-doped tin oxide (FTO) anode, which is
usually a transparent or semi-transparent material. Thus, the first
electrode is usually transparent or semi-transparent and typically
comprises FTO. Usually, the thickness of the first electrode is
from 200 nm to 600 nm, more usually, from 300 to 500 nm. For
example the thickness may be 400 nm. Typically, FTO is coated onto
a glass sheet. Often, the TFO coated glass sheets are etched with
zinc powder and an acid to produce the required electrode pattern.
Usually the acid is HCl. Often the concentration of the HCl is
about 2 molar. Typically, the sheets are cleaned and then usually
treated under oxygen plasma to remove any organic residues.
Usually, the treatment under oxygen plasma is for less than or
equal to 1 hour, typically about 5 minutes.
[0370] Usually, the second electrode comprises a high work function
metal, for instance gold, silver, nickel, palladium or platinum,
and typically silver. Usually, the thickness of the second
electrode is from 50 nm to 250 nm, more usually from 100 nm to 200
nm. For example, the thickness of the second electrode may be 150
nm.
[0371] Usually, the compact layer of an semiconductor comprises an
oxide of titanium, tin, zinc, gallium, niobium, tantalum, tungsten,
indium, neodymium, palladium or cadmium, or mixtures thereof, or a
sulphide of zinc or cadmium. Typically, the compact layer of a
semiconductor comprises TiO.sub.2. Often, the compact layer is
deposited on the first electrode. The process for producing the
photovoltaic device thus usually comprise a step of depositing a
compact layer of an n-type semiconductor.
[0372] The step of depositing a compact layer of a semiconductor
may, for instance, comprise depositing the compact layer of a
semiconductor by aerosol spray pyrolysis deposition. Typically, the
aerosol spray pyrolysis deposition comprises deposition of a
solution comprising titanium diisopropoxide bis(acetylacetonate),
usually at a temperature of from 200 to 300.degree. C., often at a
temperature of about 250.degree. C. Usually the solution comprises
titanium diisopropoxide bis(acetylacetonate) and ethanol, typically
in a ratio of from 1:5 to 1:20, more typically in a ratio of about
1:10.
[0373] Often, the step of depositing a compact layer of a
semiconductor is a step of depositing a compact layer of a
semiconductor of thickness from 50 nm to 200 nm, typically a
thickness of about 100 nm.
[0374] The photoactive layer usually comprises: (a) said porous
dielectric scaffold material; (b) said semiconductor; and (c) said
charge transporting material. Typically, the step of depositing the
photoactive layer comprises: (i) depositing the porous dielectric
scaffold material; (ii) depositing the semiconductor; and (iii)
depositing the charge transporting material. More typically, step
of depositing the photoactive layer comprises: (i) depositing the
porous dielectric scaffold material; then (ii) depositing the
semiconductor; and then (iii) depositing the charge transporting
material.
[0375] Mainly, the porous dielectric scaffold material is deposited
on to the compact layer. Usually, the porous dielectric scaffold
material is deposited on to the compact layer using a method
selected from screen printing, doctor blade coating and
spin-coating. As the skilled person will appreciate: (i) the method
of screen printing usually requires the deposition to occur through
a suitable mesh; (ii) if doctor blade coating is used, a suitable
doctor blade height is usually required; and (iii) when
spin-coating is used, a suitable spin speed is needed.
[0376] The porous dielectric scaffold material is often deposited
with an thickness of between 100 to 1000 nm, typically 200 to 500
nm, and more typically about 300 nm.
[0377] After the porous dielectric scaffold material has been
deposited, the material is usually heated to from 400 to
500.degree. C., typically to about 450.degree. C. Often, the
material is held at this temperature for from 15 to 45 minutes,
usually for about 30 minutes. This dwelling step is usually used in
order to degrade and remove material from within the pores of the
scaffold material. For instance, the dwelling step may be used to
remove cellulose from the pores.
[0378] In the step of depositing the perovskite, said perovskite is
a perovskite as described herein. The step of depositing the
perovskite usually comprises depositing the perovskite on the
porous dielectric scaffold material. Often, the step of depositing
the perovskite comprises spin coating said perovskite. The spin
coating usually occurs in air, typically at a speed of from 1000 to
2000 rpm, more typically at a speed of about 1500 rpm and/or often
for a period of from 15 to 60 seconds, usually for about 30
seconds. The perovskite is usually placed in a solvent prior to the
spin coating. Usually the solvent is DMF (dimethylformamide) and
typically the volume of solution used id from 1 to 200 .mu.l, more
typically from 20 to 100 .mu.l. The concentration of the solution
is often of from 1 to 50 vol % perovskite, usually from 5 to 40 vol
%. The solution may be, for instance, dispensed onto the porous
dielectric scaffold material prior to said spin coating and left
for a period of about 5 to 50 second, typically for about 20
seconds. After spin coating the perovskite is typically placed at a
temperature of from 75 to 125.degree. C., more typically a
temperature of about 100.degree. C. The perovskite is then usually
left at this temperature for a period of at least 30 minutes, more
usually a period of from 30 to 60 minutes. Often, the perovskite is
left at this temperature for a period of about 45 minutes.
Typically, the perovskite will change colour, for example from
light yellow to dark brown. The colour change may be used to
indicate the formation of the perovskite layer. Usually, at least
some of the perovskite, once deposited, will be in the pores of the
porous dielectric scaffold material.
[0379] Usually, the perovskite does not decompose when exposed to
oxygen or moisture for a period of time equal to or greater than 10
minutes. Typically, the perovskite does not decompose when exposed
to oxygen or moisture for a period of time equal to or greater than
24 hours.
[0380] Often the step of depositing the perovskite, may comprise
depositing said perovskite and a single-anion perovskite, wherein
said single anion perovskite comprises a first cation, a second
cation and an anion selected from halide anions and chalcogenide
anions; wherein the first and second cations are as herein defined
for said mixed-anion perovskite. For instance, the photoactive
layer may comprise: CH.sub.3NH.sub.3PbICl.sub.2 and
CH.sub.3NH.sub.3PbI.sub.3; CH.sub.3NH.sub.3PbICl.sub.2 and
CH.sub.3NH.sub.3PbBr.sub.3; CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbI.sub.3; or CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbBr.sub.3.
[0381] Alternatively, the step of depositing the perovskite, may
comprise depositing more than one perovskite, wherein each
perovskite is a mixed-anion perovskite, and wherein said
mixed-anion perovskite is as herein defined. For instance, the
photoactive layer may comprise two or three said perovskites. The
photoactive layer may comprise two perovskites wherein both
perovskites are mixed-anion perovskites. For instance, the
photoactive layer may comprise: CH.sub.3NH.sub.3PbICl.sub.2 and
CH.sub.3NH.sub.3PbIBr.sub.2; CH.sub.3NH.sub.3PbICl.sub.2 and
CH.sub.3NH.sub.3PbBrI.sub.2; CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbIBr.sub.2; or CH.sub.3NH.sub.3PbBrCl.sub.2 and
CH.sub.3NH.sub.3PbIBr.sub.2.
[0382] As a further alternative, the step of depositing a
sensitizer comprising said perovskite, may comprise depositing at
least one perovskite, for instance, at least one perovskite having
the formula (H.sub.2N.dbd.CH--NH.sub.2)PbI.sub.3zBr.sub.3(1-z).
[0383] The step of depositing a charge transporting material
usually comprises depositing a hole transporting material that is a
solid state hole transporting material or a liquid electrolyte. The
charge transporting material in the optoelectronic device of the
invention may be any suitable p-type or hole-transporting,
semiconducting material. The charge transporting material may
comprise spiro-OMeTAD
(2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene)),
P3HT (poly(3-hexylthiophene)), PCPDTBT
(Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta-
[2,1-b:3,4-bldithiophene-2,6-diyl]]), PVK (poly(N-vinylcarbazole)),
HTM-TFSI (1-hexyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide), Li-TFSI (lithium
bis(trifluoromethanesulfonyl)imide) or tBP (tert-butylpyridine).
For instance, the charge transporting material may be HTM-TFSI or
spiro-OMeTAD. Preferable, the charge transporting material is
spiro-OMeTAD. Alternatively, the charge transporting material may
be an inorganic charge transporter, for example the charge
transporting material selected from CuNSC, CuI.sub.2 and
CuO.sub.2.
[0384] Prior to the step of depositing a charge transporting
material, the charge transporting material is often dissolved in a
solvent, typically chlorobenzene. Usually the concentration of
cholorbenzene is from 150 to 225 mg/ml, more usually the
concentration is about 180 mg/ml. Typically, the hole transporting
material is dissolved in the solvent at a temperature of from 75 to
125.degree. C., more typically at a temperature of about
100.degree. C. Usually the charge transporting material is
dissolved for a period of from 25 minutes to 60 minutes, more
usually a period of about 30 minutes. An additive may be added to
the charge transporting material. The additive may be, for
instance, tBP, Li-TFSi, an ionic liquid or an ionic liquid with a
mixed halide(s).
[0385] Usually, the charge transporting material is spiro-OMeTAD.
Often, tBP is also added to the charge transporting material prior
to the step of depositing a charge transporting material. For
instance, tBP may be added in a volume to mass ratio of from 1:20
to 1:30 .mu.l/mg tBP:spiro-OMeTAD. Typically, tBP may be added in a
volume to mass ratio of about 1:26 .mu.l/mg tBP:spiro-OMeTAD.
Additionally or alternatively, Li-TFSi may be added to the charge
transporting material prior to the step of depositing a charge
transporting material. For instance, Li-TFSi may be added at a
ratio of from 1:5 to 1:20 .mu.l/mg Li-TFSi:spiro-OMeTAD. Usually
Li-TFSi may be added at a ratio of about 1:12 .mu.l/mg
Li-TFSi:spiro-OMeTAD.
[0386] The step of depositing a charge transporting material often
comprises spin coating a solution comprising the charge
transporting material onto the layer comprising said perovskite.
Usually, prior to spin coating, a small quantity of the solution
comprising the charge transporting material is deposited onto the
layer comprising said perovskite. The small quantity is usually
from 5 to 100 .mu.l, more usually from 20 to 70 .mu.l. The solution
comprising the charge transporting material is typically left for a
period of at least 5 seconds, more typically a period of from 5 to
60 seconds, prior to spin coating. For instance, the solution
comprising the charge transporting material be left for a period of
about 20 seconds prior to spin coating. The spin coating of the
charge transporting material is usually carried out at from 500 to
3000 rpm, typically at about 1500 rpm. The spin coating is often
carried our for from 10 to 40 seconds in air, more often for about
25 seconds.
[0387] The step of producing a second electrode usually comprises a
step of depositing the second electrode on to the charge
transporting material. Typically, the second electrode is an
electrode comprising silver. Often, the step of producing a second
electrode comprises placing a film comprising the hole transporting
material in a thermal evaporator. Usually, the step of producing a
second electrode comprises deposition of the second electrode
through a shadow mask under a high vacuum. Typically, the vacuum is
about 10.sup.-6 mBar. The second electrode may, for example, be an
electrode of a thickness from 100 to 200 nm. Typically, the second
electrode is an electrode of a thickness from 150 nm.
[0388] Typically, the distance between the second electrode and the
porous dielectric scaffold material is from is from 50 nm to 400
nm, more typically from 150 nm to 250 nm. Often, the distance
between the second electrode and the porous dielectric scaffold
material is around 200 nm.
[0389] Often, the process for producing an the optoelectronic
device of the invention is a process for producing a photovoltaic
device, wherein the AM1.5G 100 mWcm.sup.-2 power conversion
efficiency of the photovoltaic device is equal to or greater than
7.3%. Typically, the AM1.5G 100 mWcm.sup.-2 power conversion
efficiency is equal to or greater than 11.5%.
[0390] Typically, the process for producing an the optoelectronic
device of the invention is a process for producing a photovoltaic
device, wherein the photocurrent of the photovoltaic device is
equal to or greater than 15 mAcm.sup.-2. More typically, the
photocurrent is equal to or greater than 20 mAcm.sup.-2.
[0391] The invention is further described in the Examples which
follow.
Examples
Experimental Description
1. Synthesis of Organometal Halide Perovskites:
1.1. Preparation of Methylammonium Iodide Precursor
[0392] Methylamine (CH.sub.3NH.sub.2) solution 33 wt. % in absolute
ethanol (Sigma-Aldrich) was reacted with hydriodic acid 57 wt. % in
water (Sigma-Aldrich) at 1:1 molar ratio under nitrogen atmosphere
in anhydrous ethanol 200 proof (Sigma-Aldrich). Typical quantities
were 24 ml methylamine, 10 ml hydroiodic acid and 100 ml ethanol.
Crystallisation of methylammonium iodide (CHNH.sub.3I) was achieved
using a rotary evaporator a white coloured precipitate was formed
indicating successful crystallisation.
[0393] The methylamine can be substituted for other amines, such as
ethylamine, n-butylamine, tert-butylamine, octylamine etc. in order
to alter the subsequent perovskite properties. In addition, the
hydriodic acid can be substituted with other acids to form
different perovskites, such as hydrochloric acid.
1.2. Preparation of Methylammonium Iodide Lead (II) Chloride
(CH.sub.3NH.sub.3PbCl.sub.2I) Perovskite Solution
[0394] Methylammonium iodide (CHNH.sub.3I) precipitate and lead
(II) chloride (Sigma-Aldrich) was dissolved in dimethylformamide
(C.sub.3H.sub.7NO) (Sigma-Aldrich) at 1:1 molar ratio at 20 vol.
%.
[0395] For making different perovskites, different precursors, such
as different lead(II)halides or indeed different metals halides all
together, such as Sn iodide.
1.3. Generalising the Organometal Halide Perovskite Structure
[0396] The perovskite structure is defined as ABX.sub.3, where
A=cation (0,0,0)-ammonium ion, B=cation (1/2, 1/2, 1/2)-divalent
metal ion, and X=anion (1/2, 1/2, 0)-halogen ion. The table below
indicates possible mixed-anion peroskites.
Fixing: [A]=Methylammonium, [B]=Pb, varying [X]=any halogen
TABLE-US-00001 Perovskite Methylammonium-[X] Lead halide
(Pb[X].sub.2) CH.sub.3NH.sub.3PbBr.sub.3 CH.sub.3NH.sub.3Br
PbBr.sub.2 CH.sub.3NH.sub.3PbBrI.sub.2 CH.sub.3NH.sub.3Br PbI.sub.2
CH.sub.3NH.sub.3PbBrCI.sub.2 CH.sub.3NH.sub.3Br PbCl.sub.2
CH.sub.3NH.sub.3PbIBr.sub.2 CH.sub.3NH.sub.3I PbBr.sub.2
CH.sub.3NH.sub.3PbI.sub.3 CH.sub.3NH.sub.3I PbI.sub.2
CH.sub.3NH.sub.3PbICl.sub.2 CH.sub.3NH.sub.3I PbCl.sub.2
CH.sub.3NH.sub.3PbCIBr.sub.2 CH.sub.3NH.sub.3Cl PbBr.sub.2
CH.sub.3NH.sub.3PbI.sub.2Cl CH.sub.3NH.sub.3Cl PbI.sub.2
CH.sub.3NH.sub.3PbCl.sub.3 CH.sub.3NH.sub.3Cl PbCl.sub.2
Fixing: [A]=Methylammonium, [B]=Sn, varying [X]=any halogen
TABLE-US-00002 Perovskite Methylammonium-[X] Tin halide
(Sn[X].sub.2) CH.sub.3NH.sub.3SnBr.sub.3 CH.sub.3NH.sub.3Br
SnBr.sub.2 CH.sub.3NH.sub.3SnBrI.sub.2 CH.sub.3NH.sub.3Br SnI.sub.2
CH.sub.3NH.sub.3SnBrCI.sub.2 CH.sub.3NH.sub.3Br SnCl.sub.2
CH.sub.3NH.sub.3SnF.sub.2Br CH.sub.3NH.sub.3Br SnF.sub.2
CH.sub.3NH.sub.3SnIBr.sub.2 CH.sub.3NH.sub.3I SnBr.sub.2
CH.sub.3NH.sub.3SnI.sub.3 CH.sub.3NH.sub.3I SnI.sub.2
CH.sub.3NH.sub.3ISnICl.sub.2 CH.sub.3NH.sub.3I SnCl.sub.2
CH.sub.3NH.sub.3SnF.sub.2l CH.sub.3NH.sub.3l SnF.sub.2
CH.sub.3NH.sub.3SnCIBr.sub.2 CH.sub.3NH.sub.3Cl SnBr.sub.2
CH.sub.3NH.sub.3SnI.sub.2Cl CH.sub.3NH.sub.3Cl SnI.sub.2
CH.sub.3NH.sub.3SnCl.sub.3 CH.sub.3NH.sub.3Cl SnCl.sub.2
CH.sub.3NH.sub.3SnF.sub.2Cl CH.sub.3NH.sub.3Cl SnF.sub.2
[0397] [A] may be varied using different organic elements, for
example as in Liang et al., U.S. Pat. No. 5,882,548, (1999) and
Mitzi et al., U.S. Pat. No. 6,429,318, (2002).
1.4 Blended Perovskites
TABLE-US-00003 [0398] Perovksite 1 Perovskite 2 Outcome
CH.sub.3NH.sub.3PbICl.sub.2 CH.sub.3NH.sub.3PbIBr.sub.2 Red
CH.sub.3NH.sub.3PbICl.sub.2 CH.sub.3NH.sub.3PbBrI.sub.2 Yellow
CH.sub.3NH.sub.3PbICl.sub.2 CH.sub.3NH.sub.3PbI.sub.3 Dark brown
CH.sub.3NH.sub.3PbICl.sub.2 CH.sub.3NH.sub.3PbBr.sub.3 Yellow
CH.sub.3NH.sub.3PbBrCl.sub.2 CH.sub.3NH.sub.3PbIBr.sub.2 Yellow
CH.sub.3NH.sub.3PbBrCl.sub.2 CH.sub.3NH.sub.3PbBrI.sub.2 Yellow
CH.sub.3NH.sub.3PbBrCl.sub.2 CH.sub.3NH.sub.3PbI.sub.3 Brown
CH.sub.3NH.sub.3PbBrCl.sub.2 CH.sub.3NH.sub.3PbBr.sub.3 Yellow
1.5 Stability of Mixed-Halide Perovskites Against Single-Halide
Perovskites
[0399] The inventors have found that photovoltaic devices
comprising a mixed-halide perovskite do absorb light and operate as
solar cells. When fabricating films from the single halide
perovskites in ambient conditions. The perovskites form, but
quickly bleach in colour. This bleaching is likely to be due to the
adsorption of water on to the perovskite surface, which is known to
bleach the materials. When the complete solar cells are constructed
in ambient conditions using these single hailde perovskites, they
perform very poorly with full sun light power conversion
efficiencies of under 1%. In contrast, the mixed halide perovskites
can be processed in air, and show negligible colour bleaching
during the device fabrication process. The complete solar cell
incorporating the mixed halide perovskites perform exceptionally
well in ambient conditions, with full sun power conversion
efficiency of over 10%.
1.6 Preparation of Perovskites Comprising a Formamidinium
Cation
[0400] Formamidinium iodide (FOI) and formamidinium bromide (FOBr)
were synthesised by reacting a 0.5M molar solution of formamidinium
acetate in ethanol with a 3.times. molar excess of hydroiodic acid
(for FOI) or hydrobromic acid (for FOBr). The acid was added
dropwise whilst stirring at room temperature, then left stirring
for another 10 minutes. Upon drying at 100.degree. C., a
yellow-white powder is formed, which is then dried overnight in a
vacuum oven before use. To form FOPbI.sub.3 and FOPbBr.sub.3
precursor solutions, FOI and PbI.sub.2 or FOBr and PbBr.sub.2 were
dissolved in anhydrous N,N-dimethylformamide in a 1:1 molar ratio,
0.88 millimoles of each per ml, to give 0.88M perovskite solutions.
To form the FOPbI.sub.3zBr.sub.3(1-z) perovskite precursors,
mixtures were made of the FOPbI.sub.3 and FOPbBr.sub.3 0.88 M
solutions in the required ratios, where z ranges from 0 to 1.
[0401] Films for characterisation or device fabrication were
spin-coated in a nitrogen-filled glovebox, and annealed at
170.degree. C. for 25 minutes in the nitrogen atmosphere.
2. Insulating Mesoporous Paste:
2.1: Al.sub.2O.sub.3 Paste:
[0402] Aluminum oxide dispersion was purchased from Sigma-Aldrich
(10% wt in water) and was washed in the following manner: it was
centrifuged at 7500 rpm for 6 h, and redispersed in Absolute
Ethanol (Fisher Chemicals) with an ultrasonic probe; which was
operated for a total sonication time of 5 minutes, cycling 2
seconds on, 2 seconds off. This process was repeated 3 times.
[0403] For every 10 g of the original dispersion (1 g total
Al.sub.2O.sub.3) the following was added: 3.33 g of
.alpha.-terpineol and 5 g of a 50:50 mix of ethyl-cellulose 10 cP
and 46 cP purchased from Sigma Aldrich in ethanol, 10% by weight.
After the addition of each component, the mix was stirred for 2
minutes and sonicated with the ultrasonic probe for 1 minute of
sonication, using a 2 seconds on 2 seconds off cycle. Finally, the
resulting mixture was introduced in a Rotavapor to remove excess
ethanol and achieve the required thickness when doctor blading,
spin-coating or screen printing.
2.2 SiO.sub.2 Paste:
[0404] SiO.sub.2 particles were synthesized utilizing the following
procedure (see G. H. Bogush, M. A. Tracy, C. F. Zukoski, Journal of
Non-Crystalline Solids 1988, 104, 95.):
[0405] 2.52 ml of deionized water were added into 59.2 ml of
absolute ethanol (Fisher Chemicals). This mixture was then stirred
violently for the sequential addition of the following reactives:
0.47 ml of Ammonium Hydroxide 28% in water (Sigma Aldrich) and 7.81
ml of Tetraethyl Orthosilicate (TEOS) 98% (Sigma Aldrich). The
mixture was then stirred for 18 hours to allow the reaction to
complete.
[0406] The silica dispersion was then washed following the same
washing procedure as outlined previously for the Al.sub.2O.sub.3
paste (Example 2.1).
[0407] The amount of silica was then calculated assuming that all
the TEOS reacts. In our case, 2.1 g of SiO.sub.2 was the result of
the calculation. For every 1 g of calculated SiO.sub.2 the
following were added: 5.38 g of anhydrous terpineol (Sigma Aldrich)
and 8 g of a 50:50 mix of ethyl-cellulose 5-15 mPas and 30-70 mPas
purchased from Sigma Aldrich in ethanol, 10% by weight. After the
addition of each component, the mix was stirred for 2 minutes and
sonicated with the ultrasonic probe for 1 minute of sonication,
using a 2 seconds on 2 seconds off cycle.
3. Cleaning and Etching of the Electrodes:
[0408] The perovskite solar cells used and presented in these
examples were fabricated as follows: Fluorine doped tin oxide
(F:SnO.sub.2/FTO) coated glass sheets (TEC 15, 15 .OMEGA./square,
Pilkington USA) were etched with zinc powder and HCl (2 M) to give
the required electrode pattern. The sheets were subsequently
cleaned with soap (2% Hellemanex in water), distilled water,
acetone, ethanol and finally treated under oxygen plasma for 5
minutes to remove any organic residues.
4. Deposition of the Compact TiO.sub.2 Layer:
[0409] The patterned FTO sheets were then coated with a compact
layer of TiO.sub.2 (100 nm) by aerosol spray pyrolysis deposition
of a titanium diisopropoxide bis(acetylacetonate) ethanol solution
(1:10 titanium diisopropoxide bis(acetylacetonate) to ethanol
volume ratio) at 250.degree. C. using air as the carrier gas (see
Kavan, L. and Gratzel, M., Highly efficient semiconducting
TiO.sub.2 photoelectrodes prepared by aerosol pyrolysis,
Electrochim. Acta 40, 643 (1995); Snaith, H. J. and Gratzel, M.,
The Role of a "Schottky Barrier" at an Electron-Collection
Electrode in Solid-State Dye-Sensitized Solar Cells. Adv. Mater.
18, 1910 (2006)).
5. Deposition of the Mesoporous Insulating Metal Oxide
Scaffold:
[0410] The insulating metal oxide paste (e.g. the Al.sub.2O.sub.3
paste) was applied on top of the compact metal oxide layer
(typically compact TiO.sub.2), via screen printing, doctor blade
coating or spin-coating, through a suitable mesh, doctor blade
height or spin-speed to create a film with an average thickness of
between 100 to 1000 nm, preferably 200 to 500 nm, and most
preferably 300 nm. The films were subsequently heated to 450
degrees Celsius and held there for 30 minutes in order to degrade
and remove the cellulose, and the cooled ready for subsequent
perovskite solution deposition.
6. Deposition of the Perovskite Precursor Solution and Formation of
the Mesoporous Perovskite Semiconducting Electrode
[0411] A small volume, between 20 to 100 .mu.l of the solution of
the perovskite precursor solution in DMF (methylammonium iodide
lead (II) chloride (CH.sub.3NH.sub.3PbCl.sub.2I)) at a volume
concentration of between 5 to 40 vol % was dispensed onto each
preprepared mesoporous electrode film and left for 20 s before
spin-coating at 1500 rpm for 30 s in air. The coated films were
then placed on a hot plate set at 100 degrees Celsius and left for
45 minutes at this temperature in air, prior to cooling. During the
drying procedure at 100 degrees, the coated electrode changed
colour from light yellow to dark brown, indicating the formation of
the desired perovskite film with the semiconducting properties.
7. Hole-Transporter Deposition and Device Assembly
[0412] The hole transporting material used was spiro-OMeTAD
(Lumtec, Taiwan), which was dissolved in chlorobenzene at a typical
concentration of 180 mg/ml. After fully dissolving the spiro-OMeTAD
at 100.degree. C. for 30 minutes the solution was cooled and
tertbutyl pyridine (tBP) was added directly to the solution with a
volume to mass ratio of 1:26 .mu.l/mg tBP:spiro-MeOTAD. Lithium
bis(trifluoromethylsulfonyl)amine salt (Li-TFSI) ionic dopant was
pre-dissolved in acetonitrile at 170 mg/ml, then added to the
hole-transporter solution at 1:12 .mu.l/mg of Li-TFSI
solution:spiro-MeOTAD. A small quantity (20 to 70 .mu.l) of the
spiro-OMeTAD solution was dispensed onto each perovskite coated
mesoporous film and left for 20 s before spin-coating at 1500 rpm
for 30 s in air. The films were then placed in a thermal evaporator
where 200 nm thick silver electrodes were deposited through a
shadow mask under high vacuum (10.sup.-6 mBar).
8. Fabrication of Devices Comprising FOPbI.sub.3zBr.sub.3(1-z)
[0413] Devices were fabricated on fluorine-doped tin oxide coated
glass substrates. These were cleaned sequentially in hallmanex,
acetone, propan-2-ol and oxygen plasma. A compact layer of
TiO.sub.2 was deposited by spin-coating a mildly acidic solution of
titanium isopropoxide in ethanol. This was dried at 150.degree. C.
for 10 minutes. The TiO.sub.2 mesoporous layer was deposited by
spin-coating at 2000 rpm a 1:7 dilution by weight of Dyesol 18NR-T
paste in ethanol, forming a layer of .about.150 nm. The layers were
then sintered in air at 500.degree. C. for 30 minutes. Upon
cooling, perovskite precursors were spin-coated at 2000 rpm in a
nitrogen-filled glovebox, followed by annealing at 170.degree. C.
for 25 minutes in the nitrogen atmosphere. The hole-transport layer
was deposited by spin-coating an 8 wt. %
2,2',7,7'-tetrakis-(N,N-di-pmethoxyphenylamine)9,9'-spirobifluorene
(spiro-OMeTAD) in chlorobenzene solution with added
tert-butylpyridine (tBP) and lithium
bis(trifluoromethanesulfonyl)imide (Li-TFSI). Devices were
completed by evaporation of 60 nm Au contacts.
9. Antimony Sulphide Sensitized and Meso-Superstructured Solar
Cells
[0414] Devices comprising antimony sulphide were also fabricated.
The device fabrication was the same as for the standard dye
sensitized and perovskite meso-superstructured cells discussed
above, except for the thickness of the mesoporous layer. The
mesoporous layer was (i) .about.1.5 microns for TiO.sub.2 and (ii)
.about.700 nm for Al.sub.2O.sub.3. After sintering the mesoporous
TiO.sub.2 or Al.sub.2O.sub.3 coated substrates (FTO/compact
TiO.sub.2/mesoporous oxide) the substrates were put into a cold
chemical bath and kept at 10 deg.C. for 3 hours. The antimony
sulphide was grown on the internal surface of the meosporous films
within the chemical bath. After removing from the chemical bath,
the substrates were rinsed in deionized (DI) water and annealed at
300 deg.degree. C. in inert atmosphere (nitrogen glove box) for 30
minutes, then allowed to cool in air. The hole transporter (P3HT,
15 mg/ml in chlorobenzene) was dispensed on top of the antimony
sulphide coated substrates and spin-coated at 1000 rpm for 45
seconds to form a dry film. Electrodes were then deposited under
high vacuum via thermal evaporation to form a gold/silver 10/150 nm
cathode. The resulting cells had the structure: FTO/compact
TiO.sub.2/mesoporous oxide (TiO.sub.2 or Al.sub.2O.sub.3) coated
with antimony sulphide/P3HT/gold/silver. The cells were then tested
after leaving in air overnight.
[0415] The chemical bath deposition was carried out as follows:
0.625 mg SbCl.sub.3 was dissolved in 2.5 ml acetone. 25 ml
Na.sub.2SO.sub.3 (1M) was then slowly added, with stirring. The
volume was then made up to 100 ml by adding cold DI water, and a
few drops of HCl were added, until the resulting pH was 3.0.
[0416] The results are shown in FIGS. 13 and 14. Data for three
devices are shown: (i) a "MSSCs" or meso-superstructured solar cell
device, in which the mesoporous oxide comprises a TiO.sub.2
mesoporous single crystal electrode where the metal oxide paste was
made using the following: 165 mg TiO.sub.2 (assumed); 28 uL acetic
acid; 72 uL water; 550 mg terpineol; and 825 mg cellulose (10% in
EtOH); (ii) a "NP" or dyesol device, in which the mesoporous oxide
comprises TiO.sub.2 nanoparticles, the standard dyesol paste; and
(iii) an alumina device, in which the mesoporous oxide comprises
alumina as the porous dielectric scaffold material.
Experimental Results
[0417] The motivation of the present inventors has been to realize
a solution processable solar cell which overcomes the inherent
issues with organic absorbers and disordered metal oxides. They
have followed a similar approach to ETA solar cells, thus
capitalizing on the inorganic absorber, but entirely eliminated the
mesoporous n-type metal oxide. They have employed mesoporous
alumina as an "insulating scaffold" upon which an organometal
halide perovskite is coated as the absorber and n-type component.
This is contacted with the molecular hole-conductor,
(2,2(7,7(-tetrakis-(N,N-di-pmethoxyphenylamine)9,9(-spirobifluorene)
(spiro-OMeTAD) (U. Bach et al., Nature 395, 583-585 (1998)) which
completes the photoactive layer. The photoactive layer is
sandwiched between a semi-transparent fluorine doped tin oxide
(F:SnO.sub.2/FTO) and metal electrode to complete the device. A
schematic illustration of a cross section of a device is shown in
FIG. 1, and sketches illustrating the different layers in the solar
cell and components in the solar cell are shown in FIGS. 2 and 3.
Upon photoexcitation, light is absorbed in the perovskite layer,
generating charge carriers. Holes are transferred to the
hole-transporter and carried out of the solar cell, while the
electrons percolate through the perovskite film and are collected
at the FTO electrode. The displacement of the holes to the
hole-transporter, removes the "minority" carrier from the absorber
and is key to enabling efficient operation. Record power conversion
efficiencies of 10.9% are demonstrated under simulated AM1.5 full
sun light, representing the most efficient solid-state hybrid solar
cell reported to date. A current voltage curve for such a solar
cell is shown in FIG. 4.
Absorber and Thin Film Characterisation
[0418] The perovskite structure provides a framework to embody
organic and inorganic components into a neat molecular composite,
herein lie possibilities to manipulate material properties governed
by the atomic orbitals of the constituent elements. By
experimenting with the interplay between organic-inorganic elements
at the molecular scale and controlling the size-tunable crystal
framework cell it is possible to create new and interesting
materials using rudimentary wet chemical methods. Indeed, seminal
work by Era and Mitzi champion the layered perovskite based on
organometal halides as worthy rivals to more established materials,
demonstrating excellent performance as light-emitting diodes (H. D.
Megaw, Nature 155, 484-485 (1945); M. Era, T. Tsutsui, S. Saito,
Appl. Phys. Lett. 67, 2436-2438 (1995)) and transistors with
mobilities competitive comparable with amorphous silicon (C. R.
Kagan, D. B. Mitzi, C. D. Dimitrakopoulos, Science 286, 945-947
(1999)).
[0419] The specific perovskite the inventors introduce here is of
mixed-halide form: methylammonium iodide lead (II) chloride,
(CH.sub.3NH.sub.3PbCl.sub.2I) which is processed from a precursor
solution in N,N-Dimethylformamide as the solvent via spin-coating
in ambient conditions. Unlike the single-halide lead perovskite
absorbers previously reported in solar cells (A. Kojima, K.
Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 131, 6050-6051
(2009); J-H Im, C-R Lee, J-W Lee, S-W Park, N-G Park, Nanoscale 3,
4088-4093 (2011)), this iodide-chloride mixed-halide perovskite is
remarkably stable and easily processable in air. In FIG. 5 the
UV-Vis-NIR absorption spectra of the mixed halide perovskite in the
solar cell composite demonstrates good light harvesting
capabilities over the visible to near infrared spectrum. Also shown
is the light absorption of the active layer of a complete solar
cell sealed in a nitrogen atmosphere, during 1000 hours constant
illumination under full sunlight. Negligible change in spectra is
clearly illustrated by the inset, which shows the optical density
of the film at 500 nm remaining around 1.8 throughout the entire
measurement period (OD 1.8 corresponds to 98.4% attenuation).
Solar Cell Fabrication
[0420] To construct the solar cells fluorine doped tin oxide
(F:SnO.sub.2/FTO) is coated with a compact layer of TiO.sub.2 via
spray-pyrolysis (L. Kavan, M. Gratzel, Electrochim. Acta 40,
643-652 (1995)), which assures selective collection of electrons at
the anode. The film is then coated with a paste of alumina,
Al.sub.2O.sub.3, nanoparticles and cellulose via screen printing,
which is subsequently sintered at 500.degree. C. to decompose and
remove the cellulose, leaving a film of mesoporous Al.sub.2O.sub.3
with a porosity of approximately 70%. The perovskite precursor
solution is coated within the porous alumina film via spin-coating.
To elaborate upon this coating process, there has been extensive
previous work investigating how solution-cast materials infiltrate
into mesoporous oxides (H. J. Snaith et al., Nanotechnology 19,
424003-424015 (2008); T. Leijtens et al., ACS Nano 6, 1455-1462
(2012); J. Melas-Kyriazi et al., Adv. Energy. Mater. 1, 407-414
(2011); I-K. Ding et al., Adv. Funct. Mater. 19, 2431-2436 (2009);
A. Abrusci et al., Energy Environ. Sci. 4, 3051-3058 (2011)). If
the concentration of the solution is low enough, and the solubility
of the cast material high enough, the material will completely
penetrate the pores as the solvent evaporates. The usual result is
that the material forms a "wetting" layer upon the internal surface
of the mesoporous film, and uniformly, but not completely, fills
the pores throughout the thickness of the electrode. (H. J. Snaith
et al., Nanotechnology 19, 424003-424015 (2008); T. Leijtens et
al., ACS Nano 6, 1455-1462 (2012); J. Melas-Kyriazi et al., Adv.
Energy. Mater. 1, 407-414 (2011); I-K. Ding et al., Adv. Funct.
Mater. 19, 2431-2436 (2009); A. Abrusci et al., Energy Environ.
Sci. 4, 3051-3058 (2011)).) The degree of "pore-filling" is
controlled by varying the solution concentration (J. Melas-Kyriazi
et al., Adv. Energy. Mater. 1, 407-414 (2011); I-K. Ding et al.,
Adv. Funct. Mater. 19, 2431-2436 (2009); A. Abrusci et al., Energy
Environ. Sci. 4, 3051-3058 (2011)). If the concentration of the
casting solution is high, a "capping layer" will be formed on top
of the mesoporous oxide in addition to a high degree of
pore-filling. In the films created here, there is no appearance of
a capping layer of perovskite when the mesoporous Al.sub.2O.sub.3
films are coated with the perovskite, indicating that the
perovskite is predominantly located within the porous film. To
complete the photoactive layer, the hole-transporter, spiro-OMeTAD,
is spin-coated on top of the perovskite coated electrode. The
spiro-OMeTAD does predominantly fill the pores and forms a capping
layer on top of the whole film. The film is capped with a silver
electrode to complete the device. A schematic illustration of the
device structure is shown in FIG. 1, along with further
illustrations of the device structure in FIG. 2 and FIG. 3. We term
this type of solar cell, where the photoactive layer is assembled
upon a porous insulating scaffold as meso-superstructured solar
cells (MSSCs). A cross sectional SEM image of a complete
photoactive layer; Glass-FTO-mesoporous Al2O3-K330-spiro-OMeTAD, is
shown in FIG. 9.
Solar Cell Characterization
[0421] In FIG. 4 the current-voltage curve for a solar cell
composed of FTO-compact TiO2-mesoporous
Al.sub.2O.sub.3--CH.sub.3NH.sub.3PbCl.sub.2I
perovskite-spiro-OMeTAD-Ag measured under simulated full sun
illumination is shown. The short-circuit photocurrent is 17 mA
cm.sup.-2 and the open-circuit voltage is close to 1 V giving an
overall power conversion efficiency of 10.9%. For the most
efficient devices the open-circuit voltage is between 1 to 1.1 V.
In FIG. 6, the photovoltaic action spectrum is shown for the solar
cell, which gives a peak incident photon-to-electron conversion
efficiency above 80% and spans the photoactive region from 450 to
800 nm.
Comparison to Existing Technology
[0422] The power-conversion efficiency for this system is at the
very highest level for new and emerging solar technologies (M. A.
Green, K. Emery, Y. Hishikawa, W. Warta, E. D. Dunlop, Prog.
Photovolt. Res. Appl. 19, 565-572 (2011)), but more exciting than
the efficiency is the extremely high open-circuit voltage
generated. GaAs is the only other photovoltaic technology which
both absorbs over the visible to nearIR region and generates such a
high open-circuit voltage. The "fundamental energy loss" in a solar
cell can be quantified as the difference in energy between the
open-circuit voltage generated under full sun light and the
band-gap of the absorber (H. J. Snaith, Adv. Funct. Mater. 20,
13-19 (2010)). The theoretical maximum open-circuit voltage can be
estimated as a function of band gap following the Shockley-Queisser
treatment (I-K. Ding et al., Adv. Funct. Mater. 19, 2431-2436
(2009)), and for a material with a band gap of 1.55 eV the maximum
possible open-circuit voltage under full sun illumination is 1.3 V,
giving a minimum "loss-in-potential" 0.25 eV. In FIG. 7, the
open-circuit voltage is plotted versus the optical-band gap of the
absorber, for the "best-in-class" of most established and emerging
solar technologies. For the meso-superstructured perovskite solar
cell the optical band gap is taken to be 1.55 eV and the
open-circuit voltage to be 1.1 V. With loss-in-potential as the
only metric, the new technology is very well positioned in fourth
out of all solar technologies behind GaAs, crystalline silicon and
copper indium gallium (di)selenide. Remarkably, the perovskite
solar cells have fundamental losses than are lower than CdTe, which
is the technology of choice for the world's largest solar
company.
Perovskite Crystal Structure
[0423] The X-ray diffraction pattern, shown in FIG. 8 was extracted
at room temperature from CH.sub.3NH.sub.3PbCl.sub.2I thin film
coated onto glass slide by using X'pert Pro X-ray
Diffractometer.
[0424] FIG. 8 shows the typical X-ray diffraction pattern of the
(Methylammonium Dichloromonoiodo plumbate(II);
CH.sub.3NH.sub.3PbCl.sub.2I film on glass substrate. X-ray
diffraction pattern confirms the ABX.sub.3 type of cubic (a=b=c=90)
perovskite structure (Pm3m). CH.sub.3NH.sub.3PbCl.sub.2I gave
diffraction peaks at 14.20, 28.58, and 43.27.degree., assigned as
the (100), (200), and (300) planes, respectively of a cubic
perovskite structure with lattice parameter a) 8.835 .ANG., b)
8.835 and c) 11.24 .ANG.. A sharp diffraction peaks at (h 0 0;
where h=1-3) suggest that the films fabricated on glass substrate
were predominantly single phase and were highly oriented with the
a-axis self-assembly ["Organometal Halide Perovskites as
Visible-Light Sensitizers for Photovoltaic Cells" Akihiro Kojima,
Kenjiro Teshima, Yasuo Shirai and Tsutomu Miyasaka, J. Am. Chem.
Soc. 2009, 131, 6050].
[0425] CH.sub.3NH.sub.3.sup.+ cation cannot be assigned in the X
ray given its dynamic orientation, CH.sub.3NH.sub.3.sup.+ is
incompatible with the molecular symmetry, and hence the cation is
still disordered in this phase at room temperature. And thus, the
effective contribution of the C and N atoms to the total diffracted
intensity is very small relative to the contributions from Pb and X
(Cl and I) ["Alkylammonium lead halides. Part 2.
CH.sub.3NH.sub.3PbX.sub.3 (X=Cl, Br, I) perovskites: cuboctahedral
halide cages with isotropic cation reorientation", Osvaldkn OP and
Rodericke Wasylishenm et al. Can. J. Chem. 1990, 68, 412.].
[0426] The peak positions for the synthesised mixed
CH.sub.3NH.sub.3PbCl.sub.2I at (h,0,0) were observed to be shifted
towards lower 20 and were positioned in between the pure
methylammonium trihalogen plumbate i.e. CH.sub.3NH.sub.3PbI.sub.3
and CH.sub.3NH.sub.3PbCl.sub.3 ["Dynamic disorder in
methylammoniumtrihalogenoplumbates (II) observed by millimeter-wave
spectroscopy", A. Poglitsch and D. Weber, J. Chem. Phys. 1987, 87,
6373.] respectively, and also the increased lattice parameter
(a=8.835 .ANG.) of the CH.sub.3NH.sub.3PbCl.sub.2I film as compared
to pure "Cl" based perovskite i.e. CH.sub.3NH.sub.3PbCl.sub.3
(a=5.67 .ANG.) with the addition of "I" content gives an evidence
of the formation of mixed halide perovskite ["Optical properties of
CH.sub.3NH.sub.3PbX.sub.3 (X=halogen) and their mixed-halide
crystals", N. Kitazawa, Y. Watanabe and Y Nakamura, J. Mat Sci.
2002, 37, 3585.].
[0427] The diffraction pattern of the product contained a few
unidentified peaks, they can attributed to the various factors
including the presence of some impurity (e.g. Pb(OH)Cl,
CH.sub.3NH.sub.3X; X=Cl and/or I, or a related compounds that may
generate during the synthesis even if slightly excess of reactants
are used, and also to the hygroscopic nature of the compound which
can resultantly form unwanted impurity ["Alkylammonium lead
halides. Part 2. CH.sub.3NH.sub.3PbX.sub.3 (X=Cl, Br, I)
perovskites: cuboctahedral halide cages with isotropic cation
reorientation", Osvaldkn OP and Rodericke Wasylishenm et al. Can.
J. Chem. 1990, 68, 412.] Additionally, "I" ion present in the
lattice may split some of the peaks at room temperature given the
fact that the pure "I" based perovskite (CH.sub.3NH.sub.3PbI.sub.3)
forms tetragonal structure ["Alkylammonium lead halides. Part 1.
Isolated .about.b 1 6 i.about.on-s in
(CH.sub.3NH.sub.3).sub.4Pb.sub.16-.sub.2H.sub.2O" Beverlyr Vincent
K, Robertsont, Stanlecya merona, N Dosvaldk, Can. J. Chem. 1987,
65, 1042; "Organometal Halide Perovskites as Visible-Light
Sensitizers for Photovoltaic Cells" Akihiro Kojima, Kenjiro
Teshima, Yasuo Shirai and Tsutomu Miyasaka, J. Am. Chem. Soc. 2009,
131, 6050].
[0428] FIGS. 10 to 12 relate to perovskites comprising a
formamidinium cation and devices comprising
FOPbI.sub.3yBr.sub.3(1-y). In general, it is considered to be
advantageous to retain a 3D crystal structure in the perovskite, as
opposed to creating layered perovskites which will inevitably have
larger exciton binding energies (Journal of Luminescence 60&61
(1994) 269 274). It is also advantageous to be able to tune the
band gap of the perovskite. The band gap can be changed by either
changing the metal cations or halides, which directly influence
both the electronic orbitals and the crystal structure.
Alternatively, by changing the organic cation (for example from a
methylammonium cation to a formamidinium cation), the crystal
structure can be altered. However, in order to fit within the
perovskite crystal, the following
(R.sub.A+R.sub.X)=t {square root over (2)}(R.sub.B+R.sub.X)
geometric condition must be met: wherein R.sub.A,B,&X are the
ionic radii of ABX ions. The inventor have unexpectedly found that
formamidinium cation (FO) does indeed form the perovskite structure
in a the cubic structure in a FOPbBr.sub.3 or FOPbI.sub.3
perovskite, and mixed halide perovskites thereof
[0429] The work leading to this invention has received funding from
the European Research Council under the European Union's Seventh
Framework Programme (FP7/2007-20131 ERC grant agreement no
279881).
* * * * *